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BIO-AGRICULTURAL  LIBRARY 
UNIVERSITY  OF  CALIFORNIA 
RIVERSIDE,  CALIFORNIA  92502 


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A  TEXT  BOOK 


PHYSICS   OF   AGRICULTURE 


BY 

F.  H.  KING 

Formtrly  Professor  of  Agricultural.  PhysL  in/fffJlMverslty  of  Wisconsin 

Author  of  "The  Soil;"  "Irrigation  and  Drainage;"  "Principles  and 
Atovemedts  of  Ground  Water" 


THIRD  EDITION 

LIBRARY 

UNIVERSITY  OF  CALIFORNIA 

CITRUS  EXPdMENT  STATION 

MADISON,  Wis. 
PUBLISHED  BY  THE  AUTHOR 

1904 
All  rights  reserved 


CorrEiGHT,  1899 
Bx    F.    H.    KING 


PREFACE. 


The  great  need  of  agricultural  practices  at  the  present 
time  is  a  keener  appreciation  and  a  more  thorough  com- 
prehension of  the  principles  which  underlie  them.  The 
facts  of  agriculture  are  spread  through  so  many  and  widely 
different  fields,  and  are  so  numerous,  that  no  one  can  hope 
to  grasp  them  all  or  needs  to  do  so.  But  the  laws  and 
principles  which  control  Ms  practice  each  farmer  must 
know  before  he  can  secure  his  re-suits  with  the  greatest  cer- 
tainty and  at  the  least  cost. 

In  these  pages  the  aim  has  been  to  present  to  the  student 
who  expects  to  be  a  farmer,  some  of  the  fundamental  prin- 
ciples he  must  understand  to  become  successful.  They 
are  presented  from  the  standpoint  of  physics  rather  than 
of  chemistry  or  of  biology,  and  in  dealing  with  the  physical 
side  of  the  problems  the  burden  of  effort  has  been  to  lead 
the  student  to  see  WHY  he  should  practice  more  than 
WHAT,  and  it  is  hoped  the  student  will  pursue  the  various 
subjects  treated  in  this  spirit,  not  only  in  his  study,  but 
above  all  on  the  farm  and  in  the  field. 

The  book  has  been  written  from  the  standpoint  of  the 
general  student  and  farmer  rather  than  that  of  more  tech- 
nical scientific  agriculture  and  only  so  much  of  laboratory 
methods  and  specific  data  of  observation  are  given  as  may 
serve  to  demonstrate  the  fundamental  principles  treated. 

F.  H.  KING. 

University  of  Wisconsin, 

Madison,  Wis.,  May,  1901. 


CONTENTS. 


INTRODUCTION. 

rum. 

MATTER  AND  FORCB 6 

MOLECULAR  CONSTITUTION  OF  BODIES 6 

Distance  between  molecules,  p.  7 ;  Motions,  p.  8 ;  Size,  p.  9 ;  Rela- 
tion to  fertilizers,  p.  11 ;  to  poisons,  p.  12  ;  to  odors,  p.  13. 

How  ODORS  AND  FLAVORS  FIND  THEIR  WAY  INTO  MILK 14 

Enter  during  secretion  of  milk,  p.  14  ;  Influenced  by  feed,  p.  15 ; 
From  the  air.  p.  15 ;  Introduced  with  solids,  p.  16 ;  Developed 
after  drawn,  p.  16. 

DEODORIZING  MILK  16 

Method,  p.  16 ;  Place,  p.  17 ;  Cooling,  p.  17. 

WORK •  •  -  •      18 

ENERGY    19 

Conservation,  p.  19 ;  Source  of  the  earth's  energy,  p.  20 ;  Solar 
energy,  p.  20 ;  How  it  reaches  the  earth,  p.  21  ;  Amount,  p.  22 ; 
Rate  of  transmission,  p.  23 ;  Kinds  of  waves,  p.  23 ;  Evapora- 
tion of  water,  p.  24  ;  Chemical  changes  produced,  p.  24. 

NATURE  OK  HEAT  AND  COLD 25 

TEMPERATURE 25 

Measurement,  p.  25 ;  Accuracy  of  thermometers,  p.  26. 

UNITS  OF  WORK  AND  ENERGY 27 

Foot-pound  and  foot-ton,  p.  27 ;  Horse-power,  p.  27 ;  Unit  of  heat, 
p.  28. 

SPECIFIC   AND   LATENT   HEAT 29 

Melting  of  ice,  p.  31 ;  Evaporation  of  water,  p.  31 ;  Cooling  by 
evaporation,  p.  32 ;  Effect  of  rain  and  snow  on  domestic  ani- 
mals, p.  33 ;  Cooling  milk,  p.  34  ;  Heat  used  in  melting  and 
evaporating,  p.  35. 

SUBFACH  TENSION,  SOLUTION  AND  OSMOSIS 36 

Rise  of  water  in  capillary  tubes,  p.  37 ;  Evaporation  and  solution, 
p.  38 ;  Diffusion,  p.  40  ;  Osmosis,  p.  41 ;  Osmotic  pressure,  p.  42 ; 
Osmosis  In  plant  feeding,  p.  46 ;  Dissociation  of  salts  in  solu- 
tion, p.  48. 

PHYSICS  OF  THE  SOIL. 

CHAPTER    I. 
NATURE,  ORIGIN  AND  WASTE  OF  SOIL. 

BOILS  AND  SUBSOILS 49 

USES  OF  SOIL 50 

FORMATION  OF  SOIL 51 

Influence  of  rock  texture,  p.  51 ;  Rock  fissures,  p.  53 ;  Running 
water,  p.  54  ;  Glaciers,  p.  57  ;  Humus  soil,  p.  61 ;  Wind-formed, 
p.  63  ;  Animals,  p.  64. 


Contents.  v 

CHAPTER   IL 
CHEMICAL  AND  MINERAL  NATURE  OF  SOILS. 

PAGH. 

ESSENTIAL  CONSTITUENTS  OF  A  FERTILE  SOIL 69 

FUNCTIONS  OF  ESSENTIAL  PLANT  POODS 70 

CHEMICAL  COMPOSITION  OF  SOILS 71 

Difference  between  clayey  and  sandy,  p.  71 ;  Differences  due  to 
texture,  p.  72  ;  Between  soils  and  subsoils,  p.  72  ;  Between  clay 
and  humus,  p.  73 ;  Between  clay  and  loess,  p.  73 ;  Between 
arid  and  humid,  p.  73  ;  between  soil  and  rock,  p.  77. 

HUMUS , 76 

Of  arid  and  humid  climates,   p.   7C. 

PLANT  FOOD 79 

Amount  removed  from  soil  by  crops,  p.  79  ;  Amount  in  soil,  p.  79  ; 
Number  of  crops  produced,  p.  80 ;  Rothamstead  experiments, 
p.  81. 

NITROGEN  IN  THE  SOIL 82 

Amount  in  Manitoba  soils,  p.  82  ;  Forms  of  occurrence,  p.  83  ;  Dis- 
tribution in  soil,  p.  83  ;  Amount  as  nitric  acid,  p.  84. 

SOURCES  OF  SOIL  NITROGEN 85 

Of  humic  nitrogen,  p.  85  ;  Symbiosis,  p.  87  ;  Observations  of  Wlno- 
gradsky  and  Berthelot,  p.  88. 

NITRIFICATION   89 

DHNITUIFICATION 89 


CHAPTER    III. 

SOLUBLE  SALTS  IN  FIELD  SOILS. 

SOLUBLE  SALTS  IN  FIELD  SOILS 92 

Amount,  p.  92 ;  Amount  limiting  plant  growth,  p.  93 ;  Mode  of 
action  on  plants,  p.  93  ;  Concentration  in  Zones,  p.  94  ;  Origin, 
p.  94  ;  In  marsh  soils,  p.  95. 

LEACHING  NECESSARY  TO  FERTILE  SOILS 95 

Correction  of  alkali  lands,  p.  95  ;  Drainage  ultimate  remedy,  p.  98 ; 
Tillage  helpful,  p.  98. 

CHANGES  IN  AMOUNT  OF  SOLUBLE  SALTS 98 

With  season,  p.  98  ;  with  different  crops,  p.  99. 

NITRATES  101 

Relation  to  total  salts,  p.  101 ;  Closeness  of  plant  feeding,  p.  101 ; 
Limits  at  which  plants  turn  yellow,  p.  102 ;  In  fallow  and 
cropped  ground,  p.  103  ;  Loss  during  winter,  p.  104  ;  Influenced 
by  cultivation,  p.  105. 

PHYSICAL  EFFECTS  OF  SOLUBLE  SALTS 106 

On  movements  of  soil  moisture,  p.  106  ;  On  surface  tension,  p.  106  ; 
On  evaporation,  p.  100  ;  On  viscosity,  p.  106. 


ri  Contents. 

CHAPTER     IV. 

PHYSICAL  NATURE  OF  SOIL. 

PAGE. 

TBXTURB   OF   Son,    108 

Size  of  soil  grains,  p.  108 ;  Size  of  soil  kernels,  p.  110. 

POKE  SPACE  IN  SOIL Ill 

Determines  maximum  water  capacity,  p.  114 ;  Influences  rate  of 
percolation,  p.  115  ;  Method  of  measuring,  p.  115  ;  Largest  possi- 
ble, p.  116. 

INTERNAL  SURFACE  OF  SOILS 118 

Amount  per  gram  and  sq.  ft.,  p.  118  ;  Determination,  p.  115). 

EFFECTIVE  DIAMETER  OF  SOIL  GRAINS 121 

Method  of  determination,  p.   121 ;  Flow  of  fluids  computed  from, 

p.  123  ;  surface  computed  from,  p.  124. 
WEIGHT  OF  SOILS  127 

CHAPTER     V. 

SOIL  MOISTURE. 

CONDITIONS  OF  SOIL  MOISTURE  129 

Gravitational,  p.  329;  Capillary,  p.  130;  Hygroscopic,  p.  130. 

WATER  CONTENT  OF  SOILS 131 

Ways  of  expressing,  p.  131 ;  Maximum  capacity  of  field  soils,  p. 
131;  Capillary  capacity,  p.  132;  Influence  of  distance  above 
standing  water  on  capacity,  p.  134. 

SOIL  MOISTURE  AVAILABLE  TO  CROPS 135 

Soils  which  yield  moisture  most  completely,  p.  13G  ;  Relation  of 
thickness  of  moisture  film  to  per  cent,  of  water,  p.  137  ;  Af- 
fected by  jointed  structure,  p.  138  ;  Increased  by  open  struc- 
ture, p.  138  ;  By  drainage,  p.  139. 

AMOUNT  OF  WATEB  REQUIRED  BY  CROPS 13» 

For  different  yields  of  wheat,  p.  140 ;  Least  amount  for  different 
crops,  p.  141. 

CHAPTER  VL 
PHYSICS  OF  PLANT  BREATHING  AND  ROOT  ACTION. 

MECHANISM  AND  METHOD  OF  TRANSPIRATION 112 

Breathing  of  plants  and  animals,  p.  142  ;  Respiratory  organs  In 
plants,  p.  142  ;  Breathing  pores,  p.  143  ;  chlorophyll  cells,  p. 
143  ;  Guard  cells,  p.  143  ;  Their  action,  p.  144  ;  Loss  of  water 
through,  p.  145. 

STRUCTURE  AND  MODE  OF  ROOT  ACTION 145 

Functions  of  roots,  p.  145  ;  Absorbing  portion,  p.  146  ;  structure 
of  root  hairs,  p.  147 ;  Relation  to  soil  grains,  p.  147  ;  Method  of 
gathering  water,  p.  147 ;  Advance  through  soil,  p.  148 ;  Ex- 
tent of  root  development,  p.  150  ;  Total  root  of  plants,  p.  157. 


Contents.  vii 


CHAPTER    VII. 

MOVEMENTS  OF  SOIL  MOISTURE. 

PAQH. 

GRAVITATIONAL  MOVEMENTS    158 

Percolation,  p.  158  ;  Rate  through  sand,  p.  159  ;  Through  scil,  p. 
159  ;  Through  dry  soil,  p.  l(iO. 

CAPILLARY  MOVEMENTS 161 

Rise  in  capillary  tubes,  p.  161 ;  Rise  in  soils,  p.  163  ;  Observed 
bight  in  moist  soil,  p.  165  ;  Measurement  of  maximum  liight, 
p.  167  ;  Rate  of  rise  in  wet  soil,  p.  168  ;  In  dry  soil,  p.  168  ;  In- 
fluenced by  rain,  p.  170 :  L>y  farmyard  manure,  p.  172 ;  By 
mulches,  p.  173  ;  By  firming  the  soil,  p.  174. 

THERMAL  MOVEMENTS   175 

Hygroscopic  soil  moisture,  p.  175  ;  Movements,  p.  175  ;  Relation  to 
size  of  soil  grains,  p.  176  ;  Amount  a  soil  may  absorb,  p.  178 ; 
Internal  evaporation,  p.  179. 

CHAPTER    VIII. 

CONSERVATION  OF  SOIL  MOISTURE. 

MODES  OF  CONTROLLING  SOIL  MOISTURE  181 

Late  fall  plowing,  p.  181 :  Late  tillage  for  orchards,  p.  182 ; 
Early  fall  plowing,  p.  182  ;  Early  spring  plowing,  p.  183  ;  Ef- 
fectiveness of  mulches,  p.  185 ;  Frequency  of  cultivation,  p. 
187  ;  Cultivation  after  rains,  p.  190  ;  Depth  of  cultivation,  p. 
191 ;  Depth  and  frequency  vary  with  the  season,  p.  191 ; 
Early  harrowing  of  corn  and  potatoes,  p.  192  ;  Harrowing  and 
rolling  small  grain  after  it  is  up,  p.  192  ;  Mulches  other  than 
soil,  p.  193. 

SUBSOILING    TO    SAVE    MOISTURE 195 

Increases  water  capacity,  p.  198 ;  decreases  capillarity,  p.  199 ; 
Favors  percolation,  p.  199  ;  More  of  water  available,  p.  200. 

DANGER  FROM  GREEN  MANURING 201 

WIND-BREAKS    AND    HEDGES 202 

CHAPTER  IX. 

RELATION  OF  AIR  TO  SOIL. 

NEEDS  OF  SOIL  VENTILATION 204 

Needs  of  free  oxygen,  p.  204  ;  Fixing  of  free  nitrogen,  p.  206. 

PROCESSES  OF  SOIL  VENTILATION 207 

By  diffusion,  p.  207 ;  By  changes  of  soil  temperature,  p.  2^7 :  Pr 
changes  of  barometric  pressure,  p.  208 ;  By  wind  suction,  p. 
208 ;  By  rains,  p.  209. 

WAYS  OF  INFLUENCING  SOIL  VENTILATION 209 

Modified  by  tillage,  p.  209  ;  Reduced  by  rolling,  p.  210  ;  Increased 
by  drainage,  p.  210  ;  Modified  by  vegetation,  p.  211. 


Contents. 

CHAPTER  X. 

SOIL   TEMPERATURE. 

PAGE. 

TEMPERATURE  AT  WHICH  GROWTH  BEGINS 212 

BEST  SOIL  TEMPERATURE 212 

Influence  on  rate  of  germination,  p.  214  ;  Effect  on  root  pressure, 
p.  215  ;  On  the  formation  of  nitrates,  p.  215. 

CONDITIONS  INFLUENCING  SOIL  TEMPERATURE 215 

Specific  heat  of  soil,  p.  215  ;  Moisture  In  soli,  p.  216  ;  Color  of  soil, 
p.  217  ;  Topography,  p.  218  :  Texture  of  surface,  p.  218  ;  Tillage, 
p.  219 :  Chemical  changes,  p.  219 ;  Rains  and  percolation,  p. 
219 ;  Rate  of  evaporation,  p.  220. 

MEANS  OF  CONTROLLING  SOIL  TEMPERATURE 221 

Rolling,  p.  221 ;  Early  thorough  tillage,  p.  222  ;  Thorough  drainage, 
p.  222. 

CHAPTER  XI. 

OBJECTS,  METHODS  AND  IMPLEMENTS  OF  TILLAGE. 

OBJECTS  OF  TILLAGE 223 

TILLAGE  TO  DESTROY  WEEDS 223 

Best  time,  p.  224;  Best  tools,  p.  225;  For  early  killing,  p.  225; 
For  Intertillage.  p.  226. 

TILLAGE  TO  MODIFY  TEXTUBE 231 

Soil  texture  and  tilth,  p.  231 ;  Importance  of  good  tilth,  p.  233. 

I  low  TEXTURE  AND  TILTH  ABB  DEVELOPED 233 

The  uses  of  harrows,  p.  234  ;  The  planker.  p.  236 ;  The  roller,  p. 
237 ;  The  plow,  p.  238 ;  How  may  puddle  soils,  p.  239 ;  May 
correct  texture  and  improve  tilth,  p.  239. 

FOBMS    OF    PLOWS 239 

Must  be  adapted  to  the  soil,  p.  240 ;  Sod  plow,  p.  241 ;  Pulverizing 
plow,  p.  242 ;  Mellow  soil  plow,  p.  242. 

DBAFT  OF  PLOWS.  . .- 243 

English  and  American  trials,  p.  243 ;  Draft  of  sod  plow  with  and 
without  coulter,  p.  243 ;  Sod  compared  with  stubble  plow,  p. 
244  :  Influence  of  moisture  on  draft,  p.  244  ;  Draft  of  sulky 
plow,  p.  245 ;  Line  of  draft,  p.  246 ;  Scouring  of  plows,  p.  247. 

CARE   OF   PLOWS 247 

When  not  in  use,  p.  247 ;  Keeping  in  form,  p.  247. 

SUBSOIL  PLOW    250 

OBJECTS,  METHODS  AND  TIMES  OF  PLOWING 250 

Depth  of  plowing,  p.  250 ;  Best  condition  of  soil  for,  p.  251 ;  Treat- 
ment after  plowing,  p.  252 ;  Plowing  for  corn  in  the  fall,  p. 
252  ;  Plowing  sod,  p.  252  ;  Plowing  under  manure,  p.  253  :  Plow- 
Ing  under  green  manure,  p.  253 ;  Early  fall  plowing,  p.  254. 


Contents.  ix 

GROUND  WATER,  WELLS  AND  FARM  DRAINAGE. 
CHAPTER   XII. 

MOVEMENTS  OF  GROUND  WATER. 

PAGB. 

AMOUNT  STORED  IN  GROUND 255 

Ground  water  surface,  p.  258 :  Seepage,  p.  258 ;  Growth  of  streams, 

p.  259 :   Rise  of  ground  water  through   precipitation,   p.   260 ; 

Law  of  flow  through  sands,  p.  262  ;  Calculation  of  flow,  p.  262  ; 

Observed  and  computed  flow,  p.  264  ;  Relation  of  rate  of  flow  to 

diameter,  p.  266  ;  Relation  of  pressure  to  flow,  p.  266  ;  Observed 

rates  of  flow  in  sand   and  rock.   p.  268 ;   General   movements 

across  wide  areas,  p.  270. 

FLUCTUATIONS  IN  THE  RATE  OF  FLOW  OF  GROUND  WATER 270 

Due  to  barometric  changes,  p.  270 ;  In  springs,  p.  270 :  In  rate  of 

discharge  from  tile  drains,  p.  271 ;  Change  of  level  In  wells,  p. 

272 ;  Due  to  changes  in  soil  temperature,  p.  271. 

CHAPTER   XIII. 
FARM  WELLS. 

ESSENTIAL  FEATURES  OF  A  GOOD  WELL 275 

Capacity,  p.  275  ;  Best  geological  conditions,  p.  276 ;  Depth,  p.  283. 

CONDITIONS  INFLUENCING  CAPACITY 276 

Size  of  grains  and  pore  space,  p.  276  :    Depth  in  water-bearing  beds, 
p.  278 ;  Pressure,  p.  279 ;  Diameter  of  well,  p.  279. 

USB  OF  SAND  STRAINERS 281 

Capacity,   p.   281 ;   Compared  with  open  well,   p.   282. 

TEMPERATURE  OF  WELL  WATER 284 

WELL  CASINO  AND  TOP 284 

CHAPTER   XIV. 
PRINCIPLES  OF  FARM  DRAINAGE. 

NECESSITY  FOR  DRAINAGE 28b 

CONDITIONS  REQUIRING  DRAINAGE 287 

ADVANTAGE  OF  DRAINAGE          287 

Increases  root  room.  p.  287 :  Increases  available  moisture,  p.  288 ; 
Makes  soil  warmer,  p.  288 ;  Better  ventilation,  p.  290. 

TILE   DRAINS 290 

Essential  features  of  drain  tile,  p.  291 ;  How  water  enters  tile, 
p.  292  ;  Collars,  p.  292 ;  Depth  laid,  p.  292 ;  Distance  between 
tile  drains,  p.  296. 

CONFORMATION  OF  GROUND  WATER  ABOUT  DRAINS 294 

Rise  away  from  drains,  p.  293 ;  Observed  ground  water  surface,  p. 
296 ;  Rate  of  change  of  surface,  p.  297. 


Contents. 


PAGE. 

MOVEMENT  OP  DRAINAGE  WATER 298 

Heavy  clay  underlaid  with  sand,  p.  298 ;  Gradient,  p.  298 ;  Silt 
basin,  p.  299  ;  size  of  tile,  p.  299  ;  Practical  illustration  of  sizes 
and  lengths,  p.  301 ;  Outlets,  p.  302 ;  Joining  laterals  with 
mains,  p.  303  ;  Obstructions,  p.  303. 

LAYING  OUT  DRAINS 304 

SURFACE  DRAINAGE 306 

Construction,  p.  306  ;  Intercepting  underflow,  p.  307  :  Basins  with- 
out outlets,  p.  307.  Lands  requiring  surface  drainage,  p.  309. 


CHAPTER    XV. 

PRACTICE  OF  UNDERDRAINAGB. 

DETERMINING  LEVELS 312 

Instruments,  p.  312  ;  Method  of  leveling,  p.  313  ;  Contour  map,  p. 
315  ;  Locating  mains  and  laterals,  p.  315  ;  Determining  grade, 
p.  317 ;  Changing  from  one  grade  to  another,  p.  319. 

DIGGING  THE  DITCH 321 

Ditching  tools,  p.  321 ;  Width  of  ditch,  p.  322  ;  Bringing  bottom  to 
grade,  p.  322;  Placing  tile,  p.  324;  Filling  the  ditch,  p.  328. 

PRINCIPLES  OF  RURAL  ARCHITECTURE. 

CHAPTER   XVI. 
STRENGTH  OF  MATERIALS. 

STRENGTH  OF  POSTS 329 

Stress,  p.  329  ;  White  pine  pillars,  p.  330. 

TBANSVERSE  STRENGTH  331 

Tensile  strength,  p.  331  :  Principles,  p.  331  :  Proportional  to 
squares  of  depth,  p.  332  ;  Relation  to  length,  p.  334  ;  Break- 
Ing  constants,  p.  335 ;  Computing  loads,  p.  336 ;  Rafters,  p. 
337 ;  Safe  loads  for  horizontal  beams,  p.  337 ;  Selection  of  lum- 
ber, p.  338. 

BARN  FRAMES 338 

Braces,  p.  338  :  Constructing  timbers  from  2-inch  lumber,  p.  339 ; 
Forms  of  frames,  p.  339  ;  Plank  frame,  p.  340  ;  Balloon  frame, 
p.  340 ;  Cylindrical  frame,  p.  341. 

CHAPTER    XVII. 
WARMTH,  LIGHT  AND  VENTILATION. 

CONTROL  OF  TEMPERATURE 343 

Normal  animal  temperatures,  p.  343  :  Best  stable  temperature,  p. 
344;  Solid  masonry  walls,  p.  346;  Hollow  masonry  walls,  p. 
347;  Brick  veneered  \\alls,  p.  347;  All  wood  walls,  p.  348. 


Contents.  xi 

PAGE. 

LIGHTING  FARM.  BUILDINGS 348 

Efficiency  of  windows,  p.  348  ;  Position  of  windows,  p.  349. 

VENTILATION  OF  FARM   BUILDINGS 350 

Necessity  for  ventilation,  p.  350 ;  Carbon  dioxide,  p.  350 ;  Mois- 
ture from  lungs  and  skin,  p.  350  ;  Ammonia  and  organic  mat- 
ter, p.  351 ;  Micro-organisms  and  dust,  p.  352  ;  Bad  ventila- 
tion predisposes  to  disease,  p.  352. 

AMOUNT  OF  AIK  REQUIRED 353 

Amount  respired,  p.  353  ;  Degree  of  impurity  permissible,  p.  354  ; 
Rate  of  supply,  p.  354. 

CONSTRUCTION  OF  VENTILATORS 355 

Capacity  of  flues,  p.  355  ;  Forces  producing  ventilation,  p.  358  ;  es- 
sential features,  p.  358:  Location,  p.  359;  Place  of  openings,  p. 
360  ;  Introduction  of  fresh  air,  p.  362  ;  Construction,  p.  363  ; 
Ventilation  of  basement  stables,  p.  364. 


CHAPTER    XVIII. 
PRINCIPLES  OF  CONSTRUCTION. 

RELATION  OF  COVERING  TO  SPACE  ENCLOSED 366 

Relation  of  walls  to  floor  space,  p.  366;  Relation  of  bight  to  ca- 
pacity, p.  367  ;  Combined  and  separate  construction,  p.  370 ; 
Saving  of  labor,  p.  372. 

STABLE  FLOORS 374 

Essential  features,  p.  374  ;  Cold  and  warm  floors,  p.  375  ;  Use  of 
bedding,  p.  376  ;  Wood  floors,  p.  377  ;  Making  wood  floors  water- 
tight, p.  377 ;  Stone  floors,  p.  378 ;  Macadam  floors,  p.  378  ; 
Macadam  for  barn  yard,  p.  379. 

CONSTRUCTION  OF  CEMENT  FLOORS  AND  WALKS 379 

Kinds  of  cement,  p.  379:  Cement  concrete,  p.  379;  Materials, 
p.  380 ;  Wetting  crushed  rock.  p.  380 ;  Ratio  of  ingredients  for 
concrete,  p.  381 ;  For  finishing,  p.  381 ;  Thickness,  p.  382 ; 
Making  and  laying,  p.  382. 

CATTLE  TIES    384 

Stanchions,  p.  384;  Adjustable  stalls,  p.  385;  Movable  halter  ties, 
p.  387. 

MANGERS  388 

MANURE  DROPS   3SS 

PROVISIONS  FOR  WATERING  •  •  •  388 

Watering  in  bain,  p.  388 ;  Storing  water  in  tanks,  p.  389 ;  Water- 
ing trough,  p.  390. 
ARRANGEMENTS  FOB  UNLOADING  HAT 391 

CHAPTER  XIX. 

CONSTRUCTION  OF  SILOS. 

CONDITIONS  ESSENTIAL  FOR  PRESERVING  SILAGE 394 

Depth,  p.  394  ;    Rigid    walls,  p.  394  ;  Protection  against  frost,  p.  396. 


xii  Contents. 

PAG*. 

CONSTRUCTION  OF  STONE  SILOS 397 

Laying  walls,  p.  397 ;  Plastering,  p.  398 ;  Doors,  p.  309. 

CONSTRUCTION  OF  BRICK  SILOS 400 

Foundation,  p.  400 ;  Walls,  p.  402  ;  Tie- rods,  p.  402  ;  Making  walla 
air-tight,  p.  402 ;  Doors,  p.  403. 

CONSTRUCTION  OF  BRICK-LINED  SILOS 403 

Foundation  and  sill,  p.  405  ;  Setting  studding,  p.  405 ;  Sheeting, 
p.  405;  Siding,  p.  406;  Lining,  p.  406. 

LATHED   AND    PLASTERED    SILOS 407 

CONSTRUCTION  OF  ALL  WOOD  SILOS 409 

Foundation,  p.  409  ;  Cementing  bottom,  p.  410 ;  Sills  and  studding, 
p.  410;  Sheeting  and  siding,  p.  412;  Plate,  p.  413;  Lining, 
p.  413;  Roof,  p.  417;  Ventilation,  p.  417;  Painting  lining, 
p.  418. 

STAVE  OR  TANK   SILO 418 

Construction,  p.  420  ;  Staves,  p.  422  ;  Foundation,  p.  422  ;  Hoops, 
p.  422  ;  Doors,  p.  423. 

PIT  SILOS  423 

DIMENSION  OF  SILOS 424 

Weight  of  silage,  p.  424  ;  Capacity  of  silos,   p.  424 ;   Horizontal 

feeding  area,  p.  425. 
DANGER  IN  FILLING  SILOS 427 


FARM  MECHANICS. 

CHAPTER  XX. 
PRINCIPLES  OF  DRAFT. 

How  THB  DRAFT  INCREASES  WITH  THE  GRADE 428 

Experimental  demonstration  of  influence  of  grade  on  draft,  429. 
THE  MECHANICAL  PRINCIPLE  INVOLVED  IN  THE  RELATION  OF  DRAFT 

TO   GRADE    430 

THE  STEEPEST  GRADE  ADMISSIBLE 430 

GOOD  ROADS  MAKE  HIGH  GRADES  MORE  OBJECTIONABLE 433 

DRAFT  OF  WAGONS  ON  THE  LEVEL •  •   434 

The  smoothness  of  the  road-bed,  p.  434 ;  Rigidity  of  the  road-bed, 
p.  434 ;  Draft  of  wagons  shown  by  English  trials,  p.  436 ; 
Draft  with  different  widths  of  tire,  p.  436 ;  Size  of  the  carriage 
wheel,  p.  437 ;  Distribution  of  load  on  the  carriage,  p.  438 ; 
Heaviest  load  on  the  hind  wheels,  p.  439 ;  Direction  of  the  line 
of  draft,  p.  440 ;  Line  of  draft  on  road  wagon,  p.  441 ;  Rigidity 
of  the  carriage,  p.  442 ;  Results  of  Gen.  Morin's  experiments 
in  France,  p.  443. 

CHAPTER  XXI. 

CONSTRUCTION  AND  MAINTENANCE  OF  COUNTRY  ROADS. 

ESTABLISHING  THE  GRADE   444 

FACTORS  TO  BE  CONSIDERED  IN  ESTABLISHING  THE  GRADE 444 


Contents.  xiii 

PAOK. 

EOAD  DRAIN-AGE    445 

The  relation  of  water  to  roads,  p.  446  ;  Depth  of  under-drainage, 
p.  446  ;  Place  for  the  drain,  p.  447  ;  Fall  of  the  drain,  p.  447  ; 
Outlet  of  the  drain,  p.  448;  Size  of  tile  p.  448;  Kind  of  tile, 
p.  448 ;  Surface  drainage,  p.  448 ;  Slope  of  the  road  surface, 
p.  449  ;  Water-breaks,  p.  449. 
TEXTURE  OF  ROAD  MATERIALS 450 

Roads  should  be  built  in  layers,  p.  450  ;  Uniformity  of  size  of  ma- 
terial  used,  p.  451 ;   Shape  of  fragment,  p.  451 ;   Cleanness  of 
material,  p.  452. 
EARTH  ROADS     452 

Forming  the  road-bed,  p.  452  ;  Utilizing  the  old  road  as  a  road  bed, 
p.  455  ;  Preparing  the  road-bed  a  year  or  more  in  advance,  p. 
455  ;  Roads  on  gravelly  loam,  p.  455  ;  Roads  in  fine  clay  soil, 
p.  455  ;  Clay  roads  surfaced  with  gravel,  p.  456  ;  Sandy  roads, 
p.  456 ;  The  use  of  straw,  saw  dust  and  tan  bank  on  sandy 
roads,  p.  .457  ;  Road  gravel,  p.  457  ;  Clean  white  gravel  not  suit- 
able, p.  458  ;  Texture  of  gravel  altered  by  crushing  and  screen- 
ing, p.  458  ;  Some  gravels  contain  too  much  clay,  p.  459 ;  Gravel 
roads,  p.  459  ;  Roads  in  swainpy  places,  p.  460. 
STONE  ROADS  461 

Macadam  roads,  p.  462  ;  Construction  of  macadam  roads,  p.  462; 
Fitting  the  road-bed,  p.  463;  Forming  the  shoulders,  p.  463; 
Kinds  of  rock  for  the  road,  p.  464  ;  Foundation  and  surfacing 
stone  may  be  different,  p.  466 ;  Sorting  boulders  before  crush- 
Ing,  p.  466 ;  Using  limestone  for  binding,  p.  466 ;  Roads  made 
without  binding  material,  p.  467 ;  Use  of  sand  for  binding,  p. 
467  ;  Limestone  for  stone  roads,  p.  469 ;  Spreading  the  rock  on 
the  road-bed,  p.  470 ;  Thickness  of  layer,  p.  473 ;  Rolling,  p. 

473  ;  Size  and  weight  of  roller,  p.  473 ;  Amount  of  rolling,  p. 

474  ;  Manner  of  rolling,  p.  475  ;  Kind  of  roller,  p.  475  ,  Rock 
crusher,   p.   475 ;   Revolving  screen,   p.  477 ;   Earth  and  stone 
roads    combined,    p.    477 ;    Telford    foundation,    p.    478 ;    Cul- 
verts, p.  479. 

MAINTENANCE  OF  COUNTRY    ROADS 480 

Section  men  necessary,  p.  480 ;  Road  master,  p.  481 ;  Width  of 
tires  controlled,  p.  481 ;  Maintenance  and  repairs,  p.  482 ;  Good 
maintenance,  p.  482 ;  Maintenance  of  earth  and  gravel  roads, 
p.  483. 

CHAPTER  XXII. 

FARM  MOTORS. 

FARM   MOTORS  486 

ANIMALS  AS  MOTORS 487 

The  horse  as  a  motor,  p.  487 ;  Muscles  are  motors,  p.  487 ;  Strength 
of  muscles,  p.  488 ;  Need  of  great  muscular  strength,  p.  489 ; 
Rate  at  which  a  horse  can  generate  energy,  p.  489 ;  Horse  power 
required  to  haul  loads  on  a  wagon,  p.  490 ;  horse  power  re- 
quired to  plow,  p.  491 ;  Increased  speed  diminishes  the  traction 
power,  p.  491 ;  Diminishing  the  number  of  hours  per  day  in- 
creases the  power  of  traction,  p.  492. 


xiv  Contents. 

PAOK. 

PRINCIPLES  UNDERLYING  THE  DRAFT  OF  THE  HORSE 492 

Direction  of  the  line  of  draft,  p.  492  ;  Influence  of  weight  on  the 
draft  of  the  horse,  p.  493 ;  Influence  of  the  distribution  of 
weight  on  the  draft  of  a  horse,  494  ;  Influence  of  the  strength 
of  the  hock  muscle  on  the  draft  of  a  horse,  p.  494  ;  Influence 
of  the  width  of  the  hock  on  the  draft  of  the  horse,  p.  495  ; 
Attachment  of  the  traces  to  the  hames  at  the  shoulder,  p.  496 ; 
Two-horse  evener,  p.  49ti ;  Giving  one  horse  tne  advantage,  p. 
498  ;  Three-horse  equalizer,  p.  499. 

THE  TREAD  POWER   499 

Working  the  horse  in  the  tread  power,  p.  500. 

THE  SWEEP  POWEB 501 

STEASI  ENGINES 502 

Principle  of  action  in  the  steam  engine,  p.  502  ;  Efficiency  of  the 
steam  engine,  p.  503  ;  Pressure  of  steam  at  different  tempera- 
tures, p.  504 ;  Dry  and  wet  steam,  p.  504 :  Causes  of  water  in 
the  cylinder  of  an  engine,  p.  505 ;  Wetness  of  steam  from  the 
boiler,  p.  505  ;  Wetness  due  to  condensation  in  steam  pipes  and 
valve  chest,  p.  506  ;  Initial  condensation,  p.  506  ;  Condensation 
due  to  work  during  expansion,  p.  507  ;  Engine  boilers,  p.  508  ; 
Construction  of  steam  boilers,  p.  509 ;  Gage  cocks,  p.  510  ;  Gage 
glass,  p.  510;  Pressure  gage,  p.  511;  Safety  valve,  p.  511; 
Care  of  the  boiler,  p.  512;  Firing,  p.  513;  Foaming,  p.  513; 
Low  water  in  the  boiler,  p.  514 ;  Soft  plug,  p.  514  ;  Water  sup- 
ply, p.  515 ;  Cross-head  pump,  p.  515  ;  The  injector,  p.  515 ; 
Boiler  incrustation,  p.  517 ;  The  engine,  p.  518 ;  Governor, 
p.  521;  Lubricator,  p.  521;  Fly  wheel,  p.  522. 

GASOLINE  ENGINES    522 

Gasoline  and  steam  engines  contrasted,  p.  523 ;  Principal  parts  of 
a  gasoline  engine,  p.  523 ;  The  working  cycle,  p.  523 ;  Arrange- 
ments to  prevent  over-heating,  p.  524  :  Types  of  gasoline  en- 
gines, p.  524  ;  Cylinder,  p.  525  ;  Pumping  mechanism,  p.  525  ; 
Governor,  p.  526 ;  Valve  mechanism,  p.  528 ;  Igniting  the 
charge,  p.  529 ;  Lubrication,  p.  529 ;  Gasoline,  p.  530 ;  Size 
of  engine,  p.  530. 

WINDMILL     530 

Work  to  which  the  wind  mill  is  adapted,  p.  531 ;  Wind  pressure, 
p.  532 ;  Relation  of  wind  pressure  to  wind  velocity,  p.  532 ; 
Ability  of  wind  to  do  work,  p.  533  ;  Relation  of  diameter  of 
wheel  to  Its  efficiency,  p.  533 ;  Unsteadiness  of  wind  velocity, 
p.  534 ;  Hight  of  towers,  p.  534  ;  Observed  amount  of  work 
done  by  a  windmill  in  pumping  water,  p.  535 ;  Observed  amount 
of  work  done  by  a  windmill  In  grinding  feed,  p.  536. 


Contents.  xv 


CHAPTER  XXIIL 

FARM  MACHINES*. 

PAGE. 

FRICTION , -. 538 

Friction  between  solids,  p.  538 ;  Friction  of  rest  or  static  friction 
between  solids,  p.  539  ;  Friction  of  motion  between  solids,  p. 
539  ;  Rolling  friction,  p.  540 ;  Friction  between  liquids,  p.  540  ; 
The  action  of  lubricants,  p.  541 ;  Adaptation  of  lubricant  to 
place  of  service,  p.  541 ;  Scrupulous  cleanliness  of  bearings, 
p.  542  ;  Hot  boxes,  p.  543. 

BELTI  NG     543 

Action  of  belting,  p.  543  ;  Efficiency  of  belting,  p.  543  ;  Size  of  belt 
for  transmission  of  given  horse  power,  p.  544  ;  Condition  of 
belt,  p.  544  ;  Pulley  and  shaft,  p.  545  ;  Lacing  a  belt,  p.  545  ; 
Calculating  the  lengths  of  belts,  p.  546. 

FARM  PUMPS 546 

Suction  pump,  p.  546  ;  Size  of  piston,  p.  547  ;  Rate  of  pumping, 
p.  548  ;  Relation  of  size  of  suction  and  discharge  pipe  and  pis- 
ton to  power  required  to  work  the  pump,  p.  548  ;  Influence  of 
elbows  on  the  power  required  to  work  a  pump,  p.  550  ;  Double- 
acting  suction  pumps,  p.  550 ;  Proper  place  for  the  cylinder  in 
the  well,  p.  551. 

HYDRAULIC  RAM    .  552 


PRINCIPLES    OF    WEATHER    FORECASTING. 
CHAPTER  XXIV, 

THE  ATMOSPHERE. 

RELATION  TO  THE  EARTH  554 

Interpenetration  of  the  three  spheres,  p.  555 :  Relation  of  the  life 
zone,  p.  555. 

ATMOSPHERE 556 

Depth,  p.  556 ;  Composition,  p.  556 ;  Materials  mechanically  sus- 
pended, p.  557. 

PARTS  PLAYED  EY  THE  DIFFERENT  INGREDIENTS.  ? 557 

Oxygen,  p.  557  ;  Nitrogen,  p.  558  ;   Water,  p.  558  ;  Dust,   p.   558  ; 
Carbon  dioxide,  p.  558. 

ATMOSPHERIC  PRESSURE 559 

Applications  of  pressure,  p.  559. 
TEMPERATURE  OF  THE  ATMOSPHERE  . ,  560 


CHAPTER  XXV. 

MOVEMENTS  OF  THE  ATMOSPHERE. 
PRIMARY  CAUSE  OF  WINDS 561 


Contents. 

PAGE. 

GENERAL  CIRCULATION  OP  THE  ATMOSPHERE 562 

World  system  of  winds,  p.  562 ;  Wind  zones,  p.  563 ;  Direction  af- 
fected by  form  and  rotation  of  the  earth,  p.  564 :  Character  of 
the  winds,  p.  564  ;  Weather  of  the  wind  zones,  p.  565 ;  Shift- 
ing of  the  zones,  p.  565. 

CONTINENTAL   WINDS    568 

Influence  of  continents  on  winds,  p.  566 ;  Winds  of  January,  p. 
567 ;  Winds  of  July,  p.  567 ;  Monsoons,  p.  570. 

OBDINARY  STORMS   570 

Cyclones,  p.  570 ;  Cause  of  wind  directions,  p.  570 ;  Progressive 
movements,  p.  572 ;  Direction  of  movement,  p.  574  ;  Rate  of 
progress,  p.  574 ;  Diameters,  p.  574  ;  Duration,  p.  575 ;  Region 
of  precipitation,  p.  575 ;  Origin,  p.  576. 


CHAPTER  XXVL 
WEATHEB  CHANGES. 

PBINCIPLES  OF  FORECASTING  WEATHER  CHANGES 578 

Prevailing  winds  of  locality,  p.  578 ;  Locating  storm  center,  p. 
579  ;  Change  of  wind  direction,  p.  579  ;  Direction  of  storm  cen- 
ter, p.  579 ;  Predicting  the  course  of  the  storm  track,  p.  580 ; 
Temperature  changes,  p.  580 ;  Barometric  changes,  p.  582. 

COLD  WAVES     582 

Forecasting  warm  and  cold  weather,  p.  583. 

LONG  WARM  AND  DRY  PERIODS 583 

TBOPICAL  CYCLONES    585 

THUNDER  STORMS,  HAIL  STORMS  AND  TORNADOES 586 

Relations  to  ordinary  storms,  p.  586 ;  Tornadoes,  p.  586 ;  Schools 
of  tornadoes,  p.  588 ;  Distribution  of  thunder  showers,  p.  588 ; 
Conditions  of  formation,  p.  588 ;  Formation  of  tornadoes,  p. 
589 ;  Explosive  violence  of  tornadoes,  p.  590 ;  Unsteady  move- 
ment, p.  591 ;  Character  of  tornado  path,  p.  591 ;  Formation  of 
thunder  showers,  p.  592 ;  Formation  of  hail,  p.  592. 


INTRODUCTION, 


1.  Physics. — Briefly  defined,  physics  is  the  science  of 
Matter  and  Energy.  It  aims  to  measure  and  investigate 
the  movements  of  or  within  any  body,  whether  living  or 
dead,  endeavoring  to  show  how  the  forces  of  nature  operate 
upon  or  within  the  body  to  produce  the  phenomena  associ- 
ated with  it. 

If  we  were  endeavoring  to  ascertain  how  much  the  sun 
weighs,  how  much  energy  in  the  form  of  heat  and  light  is 
being  sent  out  from  it  daily,  or  how  this  energy  is  pro- 
duced, our  study  would  be  one  of  Solar  Physics.  If  we 
were  measuring  the  diameter  of  the  earth,  or  the  volume 
of  water  in  the  oceans ;  if  we  were  endeavoring  to  ascertain 
how  the  forces  have  operated  to  uplift  mountain  ranges  or 
to  cut  out  deep  canons  or  broad  valleys,  then  our  problem 
would  be  one  of  Terrestrial  or  Earth  Physics.  If  we  were 
measuring  the  strength  of  a  horse;  how  many  pounds  of 
feed  he  must  use  to  plow  10  acres  of  ground ;  or  endeavor- 
ing to  show  how  the  oxygen  he  breathes  and  the  food  he  eats 
give  rise  to  the  energy  of  his  muscles,  our  problem  would 
be  one  of  Animal  Physics.  If  we  were  studying  how  the 
root  forces  its  way  through  the  soil ;  how  water  is  forced 
into  and  through  the  roots  to  the  leaves  on  the  tree  or  how 
the  sunshine  breaks  down  the  carbon  dioxide  in  the  green 
chlorophyll,  our  problem  would  become  one  of  Plant  Phys- 
ics. If  we  are  endeavoring  to  determine  the  dimensions 
of  beams  to  use  in  a  barn  ;  how  heavy  a  rod  to  use  in  a  truss 
or  how  to  brace  a  building  so  that  it  may  safely  withstand 
tho  pressure  of  the  wind,  then  we  are  dealing  with  the 
Physics  of  Architecture.  And  so  we  might  go  on  enumcr- 


6  Introduction. 

ating  every  science  and  every  art  to  show  that  there  is  a 
physics  of  each  or  a  necessary  treatment  of  them  from  the 
standpoint  of  mechanical  principles  of  matter  and  energy. 
Physics,  therefore,  a  broad  science,  is  one  of  wide  applica- 
tion and  fundamentally  important  to  the  understanding  of 
almost  any  concrete  subject  when  treated  from  the  stand- 
point of  cause  and  effect. 

2.  Matter  and  Force. — So  far  as  we  are  at  present  able 
to  comprehend,  the  various  phenomena  of  nature  are  mani- 
festations of  two  classes  of  agencies,  matter  and  force.    The 
river  flowing  steadily  toward  the  sea  is  a  mass  of  matter 
urged  continually  onward  by  the  force  of  gravitation.  Coal 
and  oxygen  burning  in  the  firebox  of  the  locomotive  are  two 
forms  of  matter  urged  into  motion  by  the  force  chemical 
affinity.     The  time-keeping  watch  is  a  mechanism  of  brass 
and  steel  kept  in  uniform  motion  by  the  force  cohesion  un- 
coiling the  wound-up  spring;  and  tLe  capillary  rise  of  oil 
in  the  lamp  wick  and  of  water  through  the  soil  are  other 
movements  of  matter  actuated  by  the  same  force. 

3.  Constitution  of  Bodies. — All  bodies  or  masses  of  mat- 
ter with  which  we  are  acquainted  possess  such  properties 
as  to  make  it  appear  that  there  is  room  in  them  not  occu- 
pied by  the  essential  material  which  makes  up  the  body. 
They  are  made  out  of    definite   units   which    have    been 
named  molecules  much  as  a  bank  of  sand  is  composed  of 
grains  or  as  a  sack  of  shot  is  filled  with  spheres  of  lead. 

The  openness  of  structure  of  all  bodies  is  a  very  impor- 
tant conception  to  have  clearly  in  mind.  It  is  this  open- 
ness of  structure  which  makes  it  possible  for  foul  odors 
to  be  absorbed  by  milk  or  drinking  water;  for  moisture 
to  enter  sprouting  seeds ;  for  the  food  we  eat  to  pass  through 
the  walls  of  the  alimentary  canal  to  enter  the  blood  vessels 
and  out  of  these  again  to  the  muscles  and  nerve  centers. 
It  is  the  openness  of  structure  of  the  lung  lining  which  per- 
mits the  oxygen  of  the  air  to  enter  the  system  and  the  car- 
bonic oxide  to  escape  from  it ;  and  were  it  not  for  this  struc- 


Constitution  of  Bodies. 


ture  we  could  neither  smell  nor  taste,  for  substances  must 
penetrate  these  sense  organs  before  the  sensations  are 
awakened. 

That  there  is  unoccupied  space  in  bodies  which  appear 
to  have  a  close  structure  may  be  demonstrated  with  the  ap- 
paratus represented  in  Fig.  1.  The  bottle  is 
filled  with  water  and  into  this  is  dropped  a 
large  crystal  of  some  salt,  as  potassium  ni- 
trate or  sulfate,  or  4  teaspoonfuls  of  granu- 
lated sugar.  When  this  is  done  the  rubber 
cork  carrying  the  graduated  glass  tube  is  in- 
serted and  crowded  down  until  the  water 
rises  in  the  tube  and  stands  at  one  of  the 
graduation  marks.  If  any  change  in  volume 
occurs  with  the  solution  of  the  salt  it  will  be 
shown  by  a  rise  or  fall  of  the  water  in  the 
tube  where  the  amount  of  change  can  be  read. 
The  bottle  is  placed  in  a  large  vessel  of 
water  for  the  purpose  of  maintaining  a  con- 
stant temperature  during  the  experiment. 

The  molecules  themselves  are  made  up  of 
smaller  units  which  have  received  the  name 
of  atoms  and  the  number  of  these  atoms  Fm' 1- 
which  enter  into  the  construction  of  the  molecule  varies 
with  the  substance.  In  some  substances  the  molecule  con- 
sists of  two  atoms,  as  common  salt,  one  of  sodium  and  one 
of  chlorine,  while  the  water  molecule  contains  three  atoms, 
two  of  hydrogen  and  one  of  oxygen.  In  molecules  of  cane 
sugar  there  are  forty-five  atoms  of  three  different  kinds, 
carbon,  hydrogen  and  oxygen,  and  there  are  many  sub- 
stances having  molecules  more  complex  than  those  of  sugar. 

4.  Distances  Between  Molecules  Change  With  the  Tem- 
perature of  the  Body. — A  bar  of  iron  lengthens  and  shortens 
as  its  temperature  rises  and  falls,  and  the  wheelwright 
takes  advantage  of  the  fact  to  set  the  tires  of  the  wagon. 
This  change  of  volume  with  temperature  is  due  to  the  fact 
that  the  mean  distance  between  the  molecules  becomes 


8  Introduction. 

greater  the  higher  and  less  the  lower  the  temperature  is. 
From  this  it  follows  that  ordinarily  molecules  are  not  in 
contact  and  that  there  is  room  in  the  interior  of  bodies, 
however  compact  they  appear  to  be,  not  occupied  by  them. 
Observations  with  the  ordinary  mercurial  thermometer 
prove  the  same  general  fact.  As  the  temperature  rises 
a  portion  of  the  mercury  is  forced  out  of  the  bulb  into  the 
stem  showing  that  there  is  not  room  enough  there  for  all 
of  the  mercury  although  the  bulb  has  actually  become 
larger.  So,  too,  when  the  temperature  falls  the  mercury 
again  returns  to  the  bulb  although  the  bulb  has  itself  be- 
come smaller  than  before. 

5.  Molecules  of  Bodies  Always  in  Motion. — It  follows 
from  what  has  been  said  in  the  last  section  that  with  every 
change  of  temperature  in  bodies  their  molecules  move. 
The  general  fact  is  that  the  molecules  of  all  bodies  whose 
temperature  is  not  absolute  zero  are  in  rapid"  motion  no 
matter  whether  the  body  be  a  solid,  a  liquid  or  a  gas.  The 
higher  the  temperature  of  the  body  the  more  rapidly  do 
the  molecules  in  it  vibrate,  the  greater  is  their  rebound 
after  each  collision  and  so  the  greater  is  the  mean  distance 
between  them ;  this  is  why  most  bodies  expand  with  in- 
crease of  temperature  and  contract  when  cooling. 

It  is  the  fact  of  movement  among  molecules  which 
causes  the  diffusion  of  sugar  or  salt  through  water  after 
solution  takes  place,  which  causes  the  perfume  of  flowers 
to  be  constantly  moving  away  from  them,  which  gives  solid 
camphor  its  odor  and  which  causes  snow  and  ice  to  evapo- 
rate at  temperatures  even  below  freezing. 

The  elastic  power  of  air  in  the  bicycle  tire  is  due  to  the 
rapid  movement  of  the  molecules  and  their  frequent  and 
hard  collision  against  the  walls.  It  is  the  same  fact  which 
gives  the  steam  its  power  to  drive  the  engine.  The  larger 
the  amount  of  air  which  is  pumped  into  the  tire  of  the 
bicycle  the  greater  is  the  number  of  collisions  per  square 
inch  of  surface  per  second  and  so  the  harder  the  tire  be- 
comes. Then,  again,  when  the  wheel  is  left  in  the  hot 


Size  of  Molecules.  9 

sun  the  greater  tension  which  is  developed  is  due  to  the 
fact  that  the  absorption  of  heat  causes  all  the  molecules 
to  travel  faster,  and,  traveling  faster,  they  must  exert  a 
greater  pressure  whenever  collision  occurs  and  their  motion 
is  arrested. 

It  has  been  computed  that  the  mean  rate  at  which  the 
molecules  of  hydrogen  gas  travel  at  ordinary  temperature 
and  atmospheric  pressure  is  some  6,000  feet  per  second. 
Under  the  same  conditions  molecules  of  oxygen  gas  which 
are  16  times  as  heavy  travel  only  one-fourth  as  rapidly. 

If  it  is  difficult  to  think  of  a  body  like  a  horse-shoe  or 
a  hammer  maintaining  its  form  against  great  strains  when 
the  molecules  composing  it  are  neither  at  rest  nor  in  con- 
tact it  may  be  helpful  to  recall  the  conditions  which  exist 
in  the  solar  system.  Here  we  have  the  sun  with  all  its 
planets  and  their  satellites,  together  with  asteroids,  comets 
and  meteors,  each  in  rapid  motion  but  separated  by  im- 
mense distances,  and  yet  the  whole  system  constitutes  one 
gigantic  body  maintaining  persistently  its  form  as  it  moves 
through  space. 

6.  The  Size  of  Molecules. — Molecules  are  so  very  small 
that  it  is  extremely  difficult  to  form  any  just  conception 
of  them,  yet  there  are  many  experiments  and  observations 
which  prove  them  very  minute.  Nobcrt,  for  example, 
ruled  parallel  lines  on  glass  at  the  rate  of  101,600  per 
linear  inch,  proving  that  the  point  of  the  diamond  which 
plowed  the  furrows  must  have  been  far  less  than  roVo&ff  of 
an  inch  in  diameter. 

Lord  Kelvin  has  computed  that  the  number  of  molecules 
in  a  cubic  inch  of  any  perfect  gas  under  a  temperature 
of  32°  F.  and  a  pressure  of  30  inches  of  mercury  must  bo 
as  great  as  1023  or  ten  sextillions. 

This  is  an  enormous  number,  but  that,  there  is  a  proba- 
bility of  truth  in  it  may  be  demonstrated  by  a  simple  ex- 
periment 

Dissolve  .05  of  a  gram  of  aniline  violet  in  alcohol  and 
distribute  it  through  500  cu.  in.  of  water  in  a  large  glass 


10  Introduction. 

flask.  Pour  out  half  the  colored  water  and  fill  to  500 
cu.  in.  again.  Repeat  this  operation  as  long  as  the  eye 
can  with  certainty  detect  the  color  in  the  water.  As  many 
as  nine  divisions  may  be  made  and  the  eye  detect  the  color 
when  looking  down  through  12  inches  of  the  water  poured 
into  a  long  glass  tube  held  over  white  paper,  using  a  sim- 
ilar tube  with  clear  water  as  a  standard  for  comparison. 

If  the  division  of  the  aniline  is  carried  to  this  extent 
there  will  be  in  the  last  500  cubic  inches  of  water  only 

5l2  of  100  =  107210  of  a  Sram  of  aniline- 

It  is  reasonable  to  suppose  that  in  the  last  500  cubic 
inches  of  water  there  was  at  least  one  molecule  of  aniline 
in  each  cube  of  water  .01  of  an  inch  on  a  side,  and  if  this 
is  true  there  must  have  been  at  least 

100  X  100  X  100  X  500  =  500,000,000 

molecules  of  aniline  in  the  last  vessel  of  water.  Since  at 
least  this  number  of  molecules  is  found  in  Tsku  of  a 
gram  of  aniline  one  gram  would  contain  not  less  than 

10, 210  X  500, 000, 000  =  5, 120, 000, 000, 000  molecules. 

It  is  plain,  therefore,  from  this  straightforward  line  of 
observation  and  simple  calculation  that  molecules  of  ani- 
line at  least  must  be  very  small  and  that  a  pound  of  tho 
material  would  contain  an  enormous  number. 

From  another  line  of  observation  Maxwell  has  computed 
that  the  molecules  of  hydrogen,  oxygen  and  carbon  dioxide 
are  so  small  that  the  numbers  in  the  table  below  are  re- 
quired to  weigh  one  gram. 

Number  of  molecules  in  one  gram  of 

Hydrogen  Oxygen  Carbon  dioxido 

2,174(10)!!3  l,359(10)ss  9,881(10)3' 

That  is  to  say,  the  number  of  molecules  is  so  large  in  ono 
gram  of  these  three  substances  that  2,174,  1,359  and  9,881 


^Divisibility  of  Matter.  11 

must  be  .multiplied  by  10  used  as  a  factor  23,  22  and  21 
times  respectively  in  order  to  express  them. 

7.  Molecules  and  Commercial  Fertilizers. — It  is  a  very 
strange  fact  that  100  to  500  pounds  of  commercial  fertil- 
izers applied  to  a  poor  soil  will  produce  such  marked  ef- 
fects upon  the  growth  of  plants  when  these  small  amounts 
are  spread  over  an  acre  of  ground  and  then  dissolved  in 
and  distributed  through  the  soil  water  of  perhaps  the  en- 
tire surface  four  feet.  To  know,  however,  that  the  mole- 
cules of  these  fertilizers  are  so  extremely  small  and  that 
there  are  such  immense  numbers  of  them  in  a  single  pound 
enables  the  mind  to  better  comprehend  how  such  marked 
effects  are  possible. 

The  surface  four  feet  of  good  field  soil  when  well  supplied 
with  moisture  may  contain  the  equivalent  of  10  inches  of 
water  on  the  level.  This  amount  of  water  expressed  in 
cubic  feet  per  acre  is  3G,300.  The  experiment  with  an- 
iline indicates  that  a  single  gram  has  been  divided  into  not 
less  than  5,120,000,000,000  parts.  Let  us  compute  how 
many  parts  this  number  would  give  to  each  cubic  inch  of 
the  36,300  cubic  feet  of  soil- water  in  the  upper  four  feet 
of  an  acre. 


5, 120, 000, 000, 000_  _  fi1       , 
36,300X1,728  ' 


We  see,  thm,  that  a  single  gram  of  aniline  may  be  di- 
vided enough  to  place  81,C24  parts  in  every  cubic  inch  of 
moisture  of  an  entire  acre  of  good  soil  to  a  depth  of  four 
feet. 

But  one  gram  of  sodium  nitrate  would  contain,  accord- 
ing to  Maxwell's  results, 

NaNO3  :2  O ::  No.  of  O  molecules  :  No.  of  NaNO3  molecules 
or  85:32  ::         ],359(10)aa        :  x 

whence  x  =  51(10) 2-  =5,100,000,000,000,000,000,000,000 


12  Introduction. 

Treating  this  result  as  we  did  that  of  the  aniline  we  shall 
have 

5^00.000(000000,000,000 


as  the  number  of  molecules  of  sodium  nitrate  iu  each  cubic 
inch  of  water  from  which  the  plants  may  draw  their  sup- 
ply of  nitrogen.  It  will  be  seen  that  this  number  is  so 
large  that  even  a  cube  of  water  .01  inch  on  a  side  will 
contain  81,310,000,000,  a  number  far  too  large  for  com- 
prehension, and  yet  if  200  pounds  of  sodium  nitrate  were 
applied  to  the  acre  this  number  would  have  to  be  multiplied 
by  the  number  of  grams  in  200  pounds  to  express  the  num- 
ber of  molecules  there  would  be  for  each  cube  of  soil-water 
one-hundredth  of  an  inch  on  a  side. 

8.  Molecular  Structure  in  Relation  to  Poisons.  —  It  is  the 
extremely  large  number  of  molecules  which  may  exist  in  a 
small  space,  coupled  with  the  energy  which  these  molecules 
may  carry  with  them  in  their  movements,  which  makes 
possible  the  violent  disturbances  in  the  life  processes  of 
animals  and  plants  associated  with  the  introduction  into 
the  system  of  such  small  quantities  of  substances  known  as 
poisons.  It  will  be  easily  undei  stood  from  what  has  been 
said  regarding  the  vast  number  of  fertilizer  molecules  per 
cubic  inch  of  soil  moisture,  when  only  a  single  gram  has 
been  disseminated  throughout  the  surface  four  feet  of  a 
full  acre,  that  extremely  small  quantities  of  any  poison, 
like  strychnine,  will  contain  molecules  enough  to  charge 
the  body  of  4,lie  largest  animal  with  great  numbers  of  the 
poisonous  units. 

The  important  practical  lesson  to  be  remembered  in 
this  connection  is  that,  since  such  extremely  small  quan- 
tities of  matter,  when  introduced  into  the  plant  or  animal 
body,  are  sometimes  capable  of  producing  such  profound 
disturbances  as  to  cause  death,  extremely  small  quantities 
of  other  substances  may  have  very  important  beneficial 
effects  ;  and  it  is  quite  possible  that  it  may  be  along  such 


Odors  and  Flavors.  13 

lines  as  these  we  must  search  for  an  explanation  of  some 
of  the  little  understood  points  associated  with  the  nourish- 
ment of  both  plants  and  animals. 

9.  Ability  to  Recognize  Small  Quantities  of  Matter. — \Ve 
often  marvel  at  the  delicacy  of  the  chemical  balance  and 
many  other  instruments  of  measurement,  but  the  delicacy 
of  the  sense  organs  of  men  and  animals,  and  particularly 
the  sense  of  smell,  is  so  extreme  that  it  is  difficult  to  form 
a  just  conception  of  the  minuteness  of  the  quantity 
of  matter  or  of  energy  to  which  they  will  respond  with  the 
degree  of  intensity  which  permits  accurate  judgments  to 
be  formed. 

The  sensations  of  odors  result  from  the  disturbances 
produced  on  the  organs  of  smell  by  molecules  of  different 
substances  moving  through  the  air  when  brought  to  the 
nose.  But  when  the  blind  lady  took  the  glove  of  a  stranger 
and,  walking  up  and  down  the  aisles  of  a  large  audience 
room  filled  with  people,  handed  the  glove  to  the  owner, 
made  known  to  her  only  by  the  likeness  of  the  odor  from 
the  glove  to  that  escaping  from  the  stranger,  who  will  say 
what  fraction  of  a  gram  of  that  volatile  principle  it  was 
which  produced  so  marked  a  sensation  ?  The  weight  of 
volatile  substance  rising  into  the  air  from  a  man's  track, 
made  by  a  shoe  rather  than  his  bare  foot,  must  be  very 
small  indeed,  and  yet  the  sense  of  smell  in  the  dog  is 
so  keen  that  he  will  follow  his  master  at  a  rapid  run  even 
when  the  tracks  are  two  hours  old  and  wrhere  many  other 
people  may  have  passed  along  the  same  course  more  re- 
cently than  did  his  master. 

The  readiness  with  which  flowers,  fruits  and  vegetables 
may  be  identified  by  their  odors  alone,  often  at  consider- 
able distances,  and  with  which  animals  scent  their  enemies 
or  their  food,  are  all  of  them  concrete  demonstrations  at 
once  of  the  extreme  minuteness  and  Hast  numbers  of  mole- 
cules, while  at  the  same  time  they  prove  how  sensitive  is 
the  animal  organization  to  such  minute  quantities  of  ma- 
terial. •  •  •  • 


14:  Introduction. 

10.  Foul  Odors  and  Flavors  in  Dairy  Products. — Since  the 
commercial  value  of  dairy  products  is  determined  in  a 
high  degree  by  their  flavors  and  odors    and    since    these 
qualities  are  judged  through  the  sense  of  smell,  which  we 
have  seen  is  so  extremely  delicate  and  keen,  and  since  such 
minute  quantities  of  the  odor  or  flavor    producing    sub- 
stances are  certain  to  awaken  the  undesirable  impressions, 
it  is  clear  that  the  greatest  of  care  must  be  exercised  in 
producing,  handling  and  caring  for  them  through  all  the 
steps  preceding  the  delivery  to  the  consumer.     Since  we 
have  seen  that  so  little  fertilizer    may    be    disseminated 
through  so  much  soil  moisture  and  since  so  little  may  be  de- 
tected by  the  organs  of  smell,  it  is  plain  that  too  great  care 
cannot  be  taken  in  keeping  the  milk  clean  and  that  only 
those  who  do  this  can  hope  to  secure  the  custom  of  people 
willing  to  pay  a  high  price  for  the  milk,  cream,  butter  or 
cheese  which  just  suits  them. 

11.  How  Odors  and  Flavors  Find  Their  Way  Into  Milk. — . 
The  substances    producing    these    qualities  in  milk  make 
their  entrance  there  in  three  different  ways:  (1)  from  the 
blood  at  the  time  the  milk  is  secreted  ;  (2)  from  the  outside 
after  the  milk  is  drawn;  and  (3)  they  are  produced  within 
the  milk  after  it  has  been  secreted  before  or  after  it  is 
drawn. 

12.  Odors  Entering  Milk  During  Secretion. — Any  volatile 
principle  which  may  chance  to  be  present  in  the  blood  of 
the  animal  at  the  time  the  milk  is  being  drawn  will  find 
its  way  into  the  milk  and  will  impart  a  quality  to  it,  the 
intensity  of  the  flavor  or  odor  depending  upon  the  amount 
of  the  volatile  principle  present  and  the  readiness  with 
which  it  evaporates. 

Nearly  all  food  stuffs  contain  substances  which  produce 
odors  and  if  these  substances  are  not  destroyed  during  the 
processes  of  digestion  they  will  again  escape  from  the  body 
of  the  animal  through  the  channels  of  excretion ;  that  is, 
through  the  skin,  kidneys,  lungs,  rectum  or  udder,  and  if 


Odors  in  Milk.  15 

any  of  these  principles  still  remain  in  the  blood  at  the 
time  the  milk  is  being  drawn  they  will  appear  in  it.  It 
follows,  therefore,  that  the  longer  the  interval  of  time  be- 
tween the  taking  of  food  into  the  body  and  the  drawing 
of  the  milk  the  less  danger  there  will  be  of  the  milk  be- 
ing tainted  by  it.  The  reason  for  this  is  found  in  the  fact 
that  the  milk  is  excreted  during  the  time  of  milking  while 
the  blood  is  coursing  through  the  udder,  carrying  whatever 
odor  producing  substances  may  then  be  present. 

13.  Time  to  Feed  Odor  Producing  Foods. — It  is  clear  from 
what  has  been  said  that  if  it  is  desired  not  to  have  the 
milk  charged  with  the  undigestible  odor-principles  of  food 
while  it  is  being  drawn  these  foods  should  be  fed  as  soon 
as  possible  after  milking  and  never  just  before  in  order 
that  time  enough  may  have  elapsed  to  permit  the  odor 
principles  to  have  been  eliminated  from  the  blood  by  the 
other  organs.     On  the  other  hand,  if  the  food  contains  a 
principle  whose  odor  is  desired  in  the  milk,  then  the  re- 
verse rule  as  regards  time  of  feeding  should  be  practiced, 
namely,  to  feed  these  just  before  milking. 

14.  Introduction  of  Odors  Into  Milk  From  the  Air. — It  is 

the  fact  that  the  molecules  of  substances  are  not  in  contact 
and  that  they  are  in  motion  which  makes  it  possible  for 
milk  when  in  an  atmosphere  containing  odors  to  become 
charged  with  them.  If  the  odors  of  manure,  of  urine, 
of  ammonia,  or  any  of  those  associated  with  the  decay 
of  organic  matter  are  in  the  air  above  the  milk  the  rapid 
motion  of  these  molecules  will  cause  some  of  them  to 
plunge  into  the  milk  and  accumulate  there  until  they  be- 
come so  numerous  that  just  as  many  tend  to  escape  per 
minute  as  tend  to  enter.  The  milk  is  then  saturated  with 
the  odor  in  question. 

The  warmer  the    air    surrounding    the    milk    and    the 
warmer  the  milk  the  more  quickly  will  the  condition  oi 


16  Introduction. 

saturation  be  reached,  simply  because  the  rapidity  of  mo- 
lecular motion  increases  with  the  temperature,  for  when 
the  molecules  of  foul  odor  are  once  inside  the  warm  milk 
they  travel  or  diffuse  downward  more  rapidly  because  it 
is  warm. 

15.  Odors  and  Flavors  Resulting  From  the  Introduction  of 
Solids  Into  Milk. — It  must  be  clear  from  what  was  demon- 
strated in  (6)  that  when  great  care  is  not  taken  both  in 
keeping  the  stable  and  cows  clean  and  free  from  dust  tho 
fine  particles  of  dirt  falling  into  the  milk,  even  though 
the  amount  is  small,  may  readily  dissolve  and  impart  a 
strong  flavor  to  it,  and  one  careless    milker    may    easily 
greatly  injure  the  quality  of  that  from  the  whole  herd 
where  all  of  the  milk  is  pooled.     The  fundamental  point  to 
be  kept  ever  in  mind  is  that  a  very  little  dirt  is  capable 
of  being  divided  to  an  extreme  degree  and  that  through 
the  senses  of  taste  and  smell  extremely  small  amounts  may 
readily  be  detected. 

16.  Odors    and   Flavors   Developed   in   Milk  After  It  is 
Drawn. — Milk  is  a  very  nutritive  fluid  and  for  this  rea- 
son great  care  must  be  exercised  not  only  to  keep  dirt  out 
but  also  to  prevent  those  germs  from  entering    it    which 
have  the  power  of  developing  rapidly  there,  producing  un- 
desirable odors  and  flavors  and  thus  injuring  the  quality 
of  the  milk.     These  objectionable  germs  are  liable  to  be 
introduced  into  the  milk  through  the  dust  from  the  sta- 
ble and  the  cow  as  well  as  from  the  lack  of  proper  cleanli- 
ness of  the  vessels  in  which  the  milk  is  handled. 

17.  Deodorizing  Milk. — The  removal  of  odors  from  milk 
may  be  accomplished  by  greatly  increasing  its  surface  in 
a  space  containing  none  of  the  odors  which  the  milk  con- 
tains.    The  method  known  as  the  "Aeration  of  Milk"  has 
for  its  purpose  this  rather  than  the  exposure  of  the  milk 
to  the  air,  as  the  presence  of  the  air  hinders  the  escape  of 


Deodorizing  Milk.  17 

the  odors  rather  than  favors  it  and  if  the  milk  could  be  ex- 
posed in  a  vacuum  their  escape  would  be  more  complete  and 
more  rapid. 

The  escape  of  the  odors  from  the  milk  depends  upon  the 
rapid  motion  of  the  odor  molecules  in  it  which  forces  them 
to  escape  whenever  they  approach  the  surface  with  suffi- 
cient velocity  to  overcome  the  surface  attraction,  and  the 
division  of  the  milk  into  a  large  number  of  small  streams 
increases  the  chances  for  the  odors  to  escape  in  proportion 
to  the  increase  of  the  surface.  The  finer  the  milk  streams, 
the  farther  they  are  apart  and  the  longer  the  stream  is  in 
falling  the  more  complete  will  the  removal  of  the  odors 
be.  Where  there  can  be  a  movement  of  air  over  the  milk 
surface  or  among  the  streams  of  milk  this  will  favor  the 
removal  by  carrying  the  odor  molecules  away  and  thus 
preventing  them  from  re-entering  the  streams. 

Since  the  molecular  movement  is  greater  the  higher  the 
temperature  it  follows  that  the  deodorizing  process  should 
be  applied  as  soon  after  the  drawing  of  the  milk  as  possi- 
ble before  it  has  had  time  to  cool  and  the  molecular  motion 
to  slow  down. 

18.  Place  For  Using  the  Deodorizer — If  the  aerator  or 
deodorizer  is  used  in  the  barn  or  where  there  are  many  ob- 
jectionable odors  it  must  be  remembered  that  exactly  the 
same  conditions  which  favor  the  escape  of  the  odors  which 
the  milk  contains  when  drawn  are  the  best  conditions  to 
permit  it  to  become  charged  with  odors  from  outside,  and 
hence  the  deodorizer  or  aerator  should  be  placed  where  it 
is  surrounded  by  a  current  of  pure  air. 

19.  Cooling  Milk. — The   cooling   of   milk    immediately 
after  it  is  drawn  has  a  powerful  influence  in  preventing 
odors  from  developing  in  it  as  a  result  of  the  growth  of 
any  germs  which  may  have  found  their  way  into  the  milk 
because    the    low  temperature  makes  their  growth  much 
slower.     Cooling,  then,  is  not  a  deodorizing  process  but 
one  which  prevents  the  formation  of  new  odors.     If,  then, 


18  Introduction. 

it  is  desired  to  remove  the  animal  odors  this  if  possible 
should  be  done  first  and  then  the  milk  cooled  to  prevent 
the  formation  of  other  odors. 

20.  Work. — Whenever  any  body  is  moved  under  the  ac- 
tion of  a  force  work  is  done  and  the  amount  of  this  work 
is  measured  by  the  intensity  of  the  force  and  the  distance 
through  which  it  has  acted.  When  a  body  weighing  one 
pound  is  lifted  one  foot  against  the  attraction  of  the  earth 
the  amount  of  work  done  is  one  foot-pound.  The  same 
weight  lifted  10  feet  represents  10  foot-pounds  and  10 
pounds  raised  one  foot  has  the  same  value. 

A  team  hauling  a  load  over  a  road  under  a  mean  pull 
of  200  pounds  is  doing  200  foot-pounds  of  effective  \vork 
for  every  foot  traveled  and  in  traveling  10  miles  the  total 
work  done  is 

10  X  5,280  X  200=  10,560,000  foot-pounds. 

When  a  larger  unit  than  the  foot-pound  is  desired  that  of 
the  foot-ton  may  be  employed  and  its  value  is  2,000  pounds 
lifted  one  foot  high  or  2,000  foot-pounds.  If  a  wagon 
with  its  load  weighing  4,000  pounds  is  moved  along  the 
road  the  work  done  will  not  be  measured  by  the  product 
of  the  load  into  the  distance  traveled  but  by  the  intensity 
of  the  pull  necessary  to  pull  the  load  into  the  distance  trav- 
eled. On  a  good  level  macadam  road  60  pounds  will  move 
a  ton  and  120  pounds  two  tons.  To  draw  four  tons  over 
10  miles  of  such  level  road  means  the  doing  of 

4 X COX  IPX  5,280      R  oofi  fnnt  t, 
~ 27000"  =6, 336  foot-tons. 

So,  too,  if  the  pressure  of  steam  on  the  head  of  the  piston 
in  a  steam  engine  is  80  pounds  per  square  inch  and  the 
area  of  the  piston  is  100  square  inches  the  amount  of  work 
it  can  do  per  foot  of  stroke  is 

80  X  100  =  8,000  foot-pounds. 


Conservation  of  Energy.  19 

If  this  engine  makes  200  strokes  per  minute,  then  the  work 
it  does  per  minute  will  be 

200  X  8,000  =  1,600,000  foot-pounds. 

21.  Energy. — Energy  is  the  ability  of  a  moving  body  to 
do  work  and  the  amount  of  energy  the  moving  body  has 
is  measured  by  the  amount  of  work  it  can  be  made  to  do 
in  coming  to  rest.     If  a  weight  suspended  from  a  string 
be  drawn  to  one  side  and  then  released  it  will  begin  fall- 
ing and  acquiring  velocity,  and  on    reaching    the    lowest 
level  it  will  possess  the  ability  of  doing  a  certain  amount 
of  work.       That  amount  will  be  enough  to  raise  its  own 
weight  through  the  height  from  which  it  fell  in  the  same 
time.     If  a  bow  is  bent  and  the  string  is  released  against 
the  arrow  it  will  recover  its  form  of  rest  but  in  doing  so 
will  impart  to  the  arrow  an  amount  of  motion  equal  to  that 
which    the    bow    acquired  in  straightening  out.       When 
work  is  done  in  winding  the  clock  the  distorted  spring 
has  the  power  to  develop  an  amount  of  energy  equal  to 
that  expended  in  winding  it  up.     In  chopping  wood  the 
action  of  the  woodsman's  muscles  increases  the  amount 
of  motion  in  the  ax  until  it  falls  upon  the  wood,  when  the 
energy  which  has  been  imparted  to  it  does  the  work  of  cut- 
ting. 

We  cannot  exert  pressure  enough  with  the  hand  alone 
to  force  the  nail  into  the  board,  but  by  giving  the  muscles 
an  opportunity  to  act  gradually  upon  the  hammer  it  is 
a  simple  matter  to  store  in  it  enough  energy  to  easily  drive 
the  nail  into  the  wood.  WThen  coal  or  wood  is  burned  in 
the  fire-box  of  the  engine  and  the  heat  developed  converts 
water  into  steam  under  high  pressure  in  the  boiler  we  have 
still  another  case  where  energy  is  developed  and  accumu- 
lated in  the  rapidly  moving  molecules  of  steam  which  drive 
the  piston  whenever  the  valves  are  opened  leading  to  it. 

22.  Conservation  of  Energy — No   discovery   of  modern 
science  is  more  fundamental  than  the  fact  that  neither  mat- 
ter nor  energy  can  be  destroyed  or  created.     One  form 


20  Introduction. 

of  energy  may  be  transformed  into  another,  and  one  kind 
of  substance  may  be  decomposed  and  others  made  from  the 
components,  but  in  these  transformations  there  is  neither 
annihilation  nor  creation.  The  small  amount  of  ashes 
left  from  the  winter's  supply  of  coal  or  wood  seems  to 
point  to  a  destruction  of  matter,  but  their  weight  added 
to  that  of  the  products  which  pass  up  the  chimney  is  even 
greater  than  that  of  the  original  fuel  by  the  amount  of  oxy- 
gen which  was  required  to  burn  the  fuel.  So,  too,  the 
energy  of  10  horses  expended  in  threshing  grain  seems 
to  be  annihilated  but  it  is  only  transformed.  Heat  of  fric- 
tion and  concussion,  sound  and  material  raised  into  new 
positions,  from  which  it  may  fall,  when  added  together  will 
make  a  sum  equal  to  that  developed  by  the  horses.  Again 
we  appear  to  realize  in  the  increase  of  our  domestic  ani- 
mals or  in  milk  produced  much  less  weight  than  has  been 
used  by  them  in  feed  and  drink  but  this  is  because  such 
large  quantities  of  the  materials  eaten,  breathed  and  drank 
escape  in  an  invisible  form  through  the  skin  and  lungs. 

23.  The  Source  of  the  Earth's  Energy. — The  real  source 
of  tha  earth's  energy  is  the  sun.       All  the  rivers  of  the 
world  flowing  to  the  sea  and  the  rush  of  the  winds  swaying 
the  tree-tops  and  lashing  the  ocean  into  billows  represent 
so  much  water  and  air  lifted  from  a  lower  to  a  higher  level 
by  the  sun's  heat  and  now  being  pulled  by  gravity  back 
to  their  original  level  to  be  raised  again  and  to  again  re- 
turn, just  as  a  pendulum  rises  and  falls  while  swinging 
through  its  arc. 

The  wood  burned  in  the  stove,  the  coal  burned  in  the  en- 
gine and  the  food  consumed  by  the  horse  are  all  the  prod- 
uct of  sunshine  which  lifted  the  constituents  of  soil, 
moisture  and  air  into  such  combinations  as  readily  per- 
mits of  their  return  to  other  forms,  setting  free  the  energy 
which  was  consumed  in  producing  them. 

24.  Solar  Energy. — When  the  sun  rises  the  temperature 
increases,  usually  becoming  higher  and  higher  until  past 


Solar  Energy.  2 1 

noon,  then  when  the  sun  sets  the  temperature  falls  again, 
continuing  to  do  so  until  once  more  the  sun  is  above  the 
horizon.  So,  too,  as  our  days  grow  longer  and  longer  with 
the  approach  of  summer  in  the  middle  and  higher  lati- 
tudes, making  more  hours  of  sunshine  in  every  twenty- 
four,  the  mean  daily  temperature  increases  but  falls  away 
again  when  the  nights  became  longer  than  the  days.  Such 
and  many  other  facts  prove  the  sun  to  be  a.  source  of 
energy  which  in  some  manner  is  being  transferred  to  our 
earth.  More  than  this,  since  the  earth  travels  entirely 
around  the  sun  once  each  year  and  yet  each  day  receives 
heat  and  light  from  it,  it  follows  that  solar  energy  is  con- 
tinually leaving  the  sun  in  all  directions,  so  that  the 
amount  arrested  by  the  earth  forms  a  very  small  portion 
of  the  whole. 

25.  How  Solar  Energy  Reaches  the  Earth. — To  under- 
stand how  the  energy  of  the  sun  reaches  us,  coming  across 
93,000,000  of  miles  we  must  learn  that  the  energy  travels 
in  the  form  of  waves  through  some  medium  filling  space, 
which  has  been  named  ether,  but  whose  real  nature  is  not 
yet  understood. 

Something  similar  to  the  process  in  question  would  be 
represented  by  a  man  at  the  center  of  a  pond  throwing 
its  water  into  waves.  These  waves  would  spread  in  all 
directions  and  when  reaching  the  beach  a  portion  of  the 
energy  of  the  waves  would  be  absorbed  or  transferred  to 
whatever  body  they  chanced  to  strike.  The  energy, 
therefore,  generated  in  the  muscles,  is  changed  first  into 
wave  energy  in  the  water  and  conveyed  away  from  the 
man  in  all  directions,  but  afterward  when  arrested  at  the 
beach,  the  waves  may  move  the  pebbles,  making  them 
grind  upon  one  another,  wearing  themselves  into  sand, 
or  their  sliding  may  change  a  portion  of  the  wave  energy 
into  heat  and  thus  the  person  in  a  sjnall  degree  may  warm 
the  pebbles  lying  on  the  distant  margin  of  the  lake,  not  di- 
rectly by  the  heat  of  his  body,  but  by  the  waves  set  up  in 
3 


22 


Introduction. 


the  water,  and  much  as  the  earth  is  warmed  by  waves  sent 
out  through  the  ether  of  space  from  the  surface  of  the  sun. 
The  rapid  and  intense  molecular  motion  at  the  surface 
of  the  sun  is  transformed  into  wave  motions  in  the  sur- 
rounding ether  of  space,  as  the  motions  of  the  imaginary 
man  were  changed  into  waves  in  the  water,  and  these  ether 
waves  travel  away  from  the  sun's  surface  in  all  directions 
at  the  rate  of  186,680  miles  per  second.  So  many  of  these 
waves  as  the  size  of  the  earth  permits  it  to  stop  are  arrested 
and  transformed  into  the  various  forms  of  motion  which 
are  manifested  at  its  surface. 

26.  Amount  of  Energy  Developed  at  the  Sun's  Surface. — 
Careful  measurements  and   calculations  have    shown  that 
the  energy  developed  second  by  second  at  the  -sun's  surface, 
amounts,    according   to    Lord    Kelvin,    to    not   less    than 
133,000  horse  power  on  each  square  meter  or  1.09  square 
yards  of  its  surface. 

27.  Rate  at  Which  Solar  Energy  Reaches  the   Earth's 
Surface. — As  the  intense  energy  developed  at  the  surface  of 
the  sun  spreads  away  from    it,  it  becomes    weaker    and 
weaker  in  the  ratio  that  the  square  of  the  distance  of  the 
waves  from  the  sun  increases,  as  represented  in  Fig.  2,  and 


\ 


\ 


\ 

\ 


\ 
\ 
\ 


FIG.  2. 


BO  at  the  earth's  surface  the  amount  of  energy  has  become 
so  much  reduced  that  Lord  Kelvin  places  it  at  only  a  little 
more  than  1.3  horse  power  per  each  square  yard  of  surface. 


Solar  Energy.  23 

Cut  small  as  this  amount  of  energy  is  when  compared  with 
that  leaving  a  like  area  at  the  sun's  surface  it  is  neverthe- 
less very  large. 

It  may  seem  strange  that  so  much  energy  falling  upon 
the  earth  does  not  keep  its  surface  at  a  higher  temperature 
than  is  observed,  but  when  it  is  stated  that  the  temperature 
of  the  space  which  surrounds  the  earth  outside  its  atmos- 
phere is  — 273°  C.  and  that  only  the  thin  atmosphere 
shields  the  surface  from  this  intense  cold,  it  is  plain  that  a 
large  amount  of  heat  must  be  required  to  held  the  mean 
temperature  even  as  high  as  45°  F.  which  is 

273°  -f  7°  =  280°  C  above  absolute  zero. 

If  we  add  to  the  necessity  of  holding  the  earth's  surface  at 
a  temperature  280°  C.  to  300°  C.  above  the  space  in  which 
it  moves,  the  demand  for  energy  needed  to  maintain  the 
movements  of  water  and  of  winds,  together  with  that  em- 
bodied in  activities  of  animal  and  plant  life,  then  1.3  horse 
power  per  square  yard  of  surface  does  not  appear  so  much 
too  large. 

28.  Kinds  of  Ether  Waves. — The  energy  reaching  the 
earth  from  the  sun  in  the  form  of  wave  motion  is  not  all 
alike  in  that  the  waves  have  different  lengths,  or,  what  is 
the  same  thing,  greater  numbers  of  one  kind  reach  the 
earth  in  a  unit  of  time.  Waves  which  are  so  frequent  that 
from  392  to  757  billions  reach  us  per  second  produce  the 
sensation  of  light  when  falling  upon  the  eye;  the  slower 
ones  producing  red  light  and  the  more  rapid  ones  the  ex- 
treme violet  colors  of  the  rainbow.  Associated  with  these 
color  waves  there  are  many  other  dark  waves  to  which  the 
human  eye  is  not  sensitive.  Some  of  these  are  much 
shorter  than  the  color  waves  and  are  especially  powerful 
in  breaking  down  the  molecular  structure  of  different  sub- 
stances; that  is,  in  producing  chemical  changes  such  as  oc- 
cur on  the  photographer's  plate  when  the  negative  is  made 
and  such  as  take  place  in  the  green  parts  of  plants  when  car- 


24  Introduction. 

bon  dioxide  is  broken  down  and  the  chemical  changes  are 
produced  which  result  in  building  the  sugars,  starches  and 
cellulose  of  plants.  Others  of  these  waves  are  much  longer 
than  the  light  waves  and  these  have  a  wonderful  power  in 
producing  heating  effects  when  they  fall  upon  certain  sub- 
stances, one  of  which  is  water. 

When  bright  sunshine  is  allowed  to  pass  through  a 
large  lens  the  glass  is  but  little  warmed  by  the  passage, 
but  if  paper  is  held  at  the  light  focus  it  is  quickly  set  on 
fire  by  the  dark  or  invisible  rays.  That  it  is  the  dark  rays 
may  be  proved  by  allowing  the  light  to  pass  first  through  a 
solution  of  iodine  in  bisulphide  of  carbon  which  permits 
the  dark  waves  to  easily  pass  while  it  cuts  down  or  stops 
the  light  waves.  When  these  dark  waves  are  brought  to 
a  focus  in  water  it  is  made  to  boil  quickly  under  their  in- 
fluence. 

On  the  other  hand  if  sunlight  is  first  passed  through  a 
solution  of  alum  in  water,  which  stops  the  dark  waves  but 
allows  the  light  waves  to  pass,  then  when  they  are  focused 
upon  water  but  little  heating  effect  is  noted. 

29.  How  Water  is  Evaporated. — It  is  the  fact  that  water 
does  not  allow  the  long  dark  waves  from  the  sun  to  pass 
readily  through  it  which  causes  it  to  evaporate  so  rapidly 
from  t>cean,  lakes  and  streams,  and  from  the  soil  and  the 
leaves  of  vegetation.     When  these  waves  fall  upon  water 
they  set  its  molecules  in  such  rapid  vibration  that  the  sur- 
face tension,  or  force  of  cohesion,  is  overcome  and  many  of 
the  water  molecules  are  thrown  out  into  the  air  in  the  form 
of  invisible  vapor.     Were  the  water  not  so  opaque  to  the 
dark  waves,    neither  snow  nor    ice  would  be    as    rapidly 
melted  in  the  spring  nor  would  there  be  so  much  evapora- 
tion from  the  ocean  as  we  now  have,  hence  rains  would  be 
less  frequent  and  the  land  less  productive. 

30.  How    Chemical    Changes    Are    Produced    by  Ether 
Waves. — When  the  light  waves  and  especially  the  shorter 
dnrk  waves  fall  upon  many  substances  they  appear  to  set 


Heat  and  Temperature.  25 

up  vibrations  within  the  molecules  themselves,  which  in 
time  may  become  so  intense  as  to  overcome  the  force  by 
which  the  components  are  bound  together  and  the  molecule 
is  thrown  into  parts,  setting  them  free  so  that  when  their 
motion  slows  down  they  may  join  in  new  combinations. 
It  is  much  as  if  some  giant  power  were  to  seize  upon  a  steel 
chain,  throwing  it  into  such  intense  vibrations  that  its  sev- 
eral links  are  broken. 

31.  Nature   of  Heat  and   Cold. — When  a  body  becomes 
warm  the  rate  of  vibration  of  the  molecules  which  compose 
it  is  increased   and  the  path   through   which    they    move 
becomes  longer.       If  the  body  becomes  cold  the  rate  of 
movement  of  the  molecules  becomes  less  rapid  and  the  dis- 
tance through  which  they  move  less.     The  higher  the  rate 
of  molecular  motion  within  a  given  body  the  warmer  that 
body  is  and  vice  versa.     If  the  molecular  motion  of  a  body 
could  be  completely  brought  to  rest  its  temperature  would 
be  absolute  zero.     Under  this  condition  it  is  supposed  that 
any  body  would  have  its  smallest  volume;  and  all  liquids 
and  gases  would  become  solid. 

32.  Temperature. — When  the  temperature  of  a  body  is 
given  it  is  intended  to  state  the  degree  of  molecular  vibra- 
tion within  it.       The  temperature  at  which  a  Fahrenheit 
thermometer  marks  zero  is  not  that  of  no  molecular  motion 
but  simply  32  degrees  of  that  scale  slower  than  the  rate  at 
which  pure  water  becomes  a  solid;  while  zero  indicated  by 
a  Centigrade  thermometer  is  the  rate  of  molecular  motion 
which  permits  water  to  become  solid  and  is  a  temperature 
273  degrees  above  what  is  assumed  to  be  absolute  zero  or 
the  condition  of  absolute  rest. 

33.  How  Temperature  is  Measured. — It  is  a  general  law 
that  those  substances  which  may  exist  as  solids,  as  liquids 
or  as  gases,  as  is  the  case  with  water,  which  we  know  as  ice, 
water  and  steam,  or  invisible  vapor,  change  from  the  solid 
to  the  liquid  form  and  from  the  liquid  to  the  gaseous  form 
when  the  rate  of  molecular  motion  has  reached  a  certain 


26  Introduction. 

degree,  and  this  being  true  the  freezing  and  boiling  points 
of  various  substances  may  be  taken  as  standards  of  tem- 
perature. 

Water  being  a  common  substance  which  changes  its  state 
at  convenient  and  common  rates  of  molecular  motion  has 
been  selected  to  fix  two  degrees  of  temperature  called  the 
freezing  and  boiling  points  of  water.  When  a  thermom- 
eter scale  is  to  be  graduated  its  bulb  js  placed  under  the  in- 
fluence of  melting  or  freezing  water,  and  the  place  at  which 
the  moving  point  comes  to  rest  marked ;  then  it  is  placed 
under  the  conditions  of  boiling  water  and  the  new  point 
also  marked.  The  space  between  these  two  points  on  the 
scale  is  then  divided  into  80,  100  or  180  divisions,  accord- 
ing to  the  system  which  it  is  designed  to  follow.  Since  this 
range  in  molecular  vibration  is  divided  into  180  degrees  on 
the  Fahrenheit  scale  its  degrees  are  the  shortest,  while 
those  of  the  Reaumer  scale  are  the  longest  because  the  same 
range  is  divided  into  but  80  divisions. 

The  Centigrade  and  the  Fahrenheit  scales  are  the  two 
commonly  used  in  this  country,  the  degree  gf  the  former 
being  equal  to  I  of  the  latter. 

34.  Accuracy  of  Thermometers. — The  bulbs  of  most  ther- 
mometers shrink  after  they  are  blown  and  if  they  have  not 
been  permitted  to  stand  for  a  number  of  years  to  season 
before  fixing  the  zero  and  boiling  points  of  the  scale,  these 
points  will  change  and  the  thermometer  will  give  incorrect 
readings  in  time  and  the  cheaper  grades  of  thermometers 
are  liable  to  be  subject  to  this  error. 

The  accuracy  of  the  freezing  point  may  be  approxi- 
mately tested  by  surrounding  the  bulb  with  snow  or 
crushed  ice  out  of  which  the  melted  water  may  drain,  al- 
lowing the  thermometer  to  remain  until  the  temperature 
becomes  stationary. 

The  accuracy  of  the  boiling  point  may  also  be  approxi- 
mately determined  by  holding  the  bulb  in  rapidly  boiling 
soft  water. 


Foot-Pound  and  Horse-Power.  27 

A  thermometer  may  be  correct  at  the  freezing  and  boil- 
ing points  and  inaccurate  at  most  intervening  degrees, 
growing  out  of  the  unequal  diameter  of  the  tube  in  differ- 
ent portions  and  the  fact  that  all  degree  marks  may  be 
made  of  the  same  length.  Errors  of  this  sort  can  be  de- 
tected only  by  comparing  the  thermometer  with  a  standard. 

35.  Units  of  Work  and  Energy. — It  has  been  found  neces- 
sary in  dealing  with  the  numerical  relations  of  work  and 
energy  to  adopt  standards  of  measurement  just  as  has  been 
done  for  lengths,  volumes,  surfaces  and  mass,  and  various 
units  are  in  use. 

36.  Foot-pound  and  Foot-ton. — A  common  unit  of  work 
is  the  foot-pound,  which  is  a  mass  or  weight  of  one  pound 
lifted  vertically  against  or  in  opposition  to  the  force  of 
gravity. 

If  a  body  is  moved  one  foot  in  any  other  direction  than 
against  the  force  of  gravity  and  the  intensity  of  the  pull 
or  push  necessary  to  do  this  is  equal  to  that  required  to  lift 
one  pound,  then  in  this  case  the  work  done  is  one  foot-', 
pound.  If  2,000  pounds  is  lifted  one  foot  high  then  2,000 
foot-pounds  of  work  have  been  done,  and  this  is  sometimes 
designated  a  foot-ton.  The  same  intensity  of  pull  in  any 
other  direction  may  be  expressed  in  the  same  terms. 

Time  is  not  a  factor  taken  into  account  in  simply  ex- 
pressing the  amount  of  work  done  for  the  reason  that  a 
very  small  force  when  permitted  to  act  for  a  very  long 
time  may  raise  the  same  weight  through  one  foot,  which 
would  require  a  very  intense  force  if  permitted  to  act  but 
a  very  short  time. 

37.  Horse-power. — When  the  rate- at  which  work  is  done 
and  the  intensity  of  the  fagee  required  to  do  the  work  at 
the  stated  rate  are  to    be  expressed  quantitively,    then  a 
unit  involving  time  must  be  chosen  and  the  horse-power 
is  one  of  these.       The  horse-power  used  by  English  and^ 
American  engineers  is -the  amount  of  energy  which  can 
do  550  foot-pounds   of  work   per  second  or  33,000   foot- 


28  Introduction. 

pounds  per  minute,  equal  to  16.5  foot-tons  in  the  same 
time.  To  raise  grain  in  an  elevator  to  a  hight  of  20  feet 
at  the  rate  of  16.5  tons  per  minute  would  require  20  horse- 
power. 

If  a  horse  is  walking  2.5  miles  per  hour  and  exerting  a 
steady  pull  on  his  traces  of  100  pounds  then  the  effective 
energy  he  is  devdoping  is 

100  X  5. 280  X  2.5  _ 
GO  X  60  X  550 

and  this  for  a  well  fed  horse  weighing  1,000  pounds,  work- 
ing 10  hours  per  day  at  the  rate  of  2.5  miles  per  hour,  is 
called  a  fair  day's  work.  If  a  1,500-pound  horse  could 
do  work  in  proportion  to  his  weight  then  his  ability  to  de- 
velop energy  would  be  equal  to  the  standard  English  horse- 
power of  550  foot-pounds  per  second.  Gen.  Morin,  how- 
ever, has  placed  the  ability  of  the  average  horse  to  do  work 
at  the  rate  of  435.8  foot-pounds  per  second. 

38.  Heat  Unit — In  the  steam  engine  the  energy  of  heat 
is  converted  into  work,  and  since  heat  is  a  form  of  molecu- 
lar motion  its  quantity  must  have  a  fixed  relation  to  the 
temperature  of  a  given  amount  of  material.     The  English 
and  American  heat  unit  is  the  amount  of  heat  energy  which 
is  required  to  raise  the  temperature  of  one  pound  of  pure 
water  from  32°  F.  to  33°  F.,  and  since  one  form  of  energy 
may  be  converted  into  another  the  value  of  a  heat  unit  may 
be  expressed  in  foot-pounds.     The  English  scientist,  Joule, 
was  the  first  to  measure  the  number  of  foot-pounds  of  work 
which  one  heat  unit  could  do  and  found  it  to  be  772,  which 
when  corrected  for  the  mercurial  thermometer  became  at 
15°  C.  775  foot-pounds.  Rowland  obtained  the  value  778.3 
foot-pounds.     This  means  that  the  source  of  heat  which  ia 
able  to  raise  the  temperature  of  one  pound  of  water  one 
degree  every  second   would  also  be  able    to    raise    778.3 
pounds  one  foot  high  in  the  same  time. 

39.  Determination  of  the  Mechanical  Equivalent  of  Heat. 
— In  order  to  ascertain  the  value  of  the  heat  unit  in  foot- 


Specific  and  Latent  Heat.  29 

pounds,  Joule  arranged  a  vessel  containing  water  in  such 
a  way  that  by  means  of  nicely  adjusted  weights  he  could 
cause  them  to  drive  a  set  of  paddles  in  the  water  and  by  the 
mechanical  agitation  warm  it.  By  knowing  the  number 
of  pounds  in  his  weights,  the  distance  they  were  allowed 
to  fall  and  the  rise  in  temperature  which  was  observed  in 
a  given  weight  of  water,  he  found  the  relation  to  be  that 
stated  in  (38). 

40.  Specific  Heat. — We  have  learned  (32)  that  tempera- 
ture is  a  measure  of  the  rate  of  molecular  motion  within  a 
given  body ;  it  is  not,  however,  a  measure  of  the  amount  of 
work  which  must  be  done  upon  that  body  to  change  its 
temperature  through  a  given  number  of  degrees ;  neither  is 
it  a  measure  of  the  amount  of  work  which  may  be  secured 
from  that  body  \vhen  its  temperature  falls  a  given  amount. 

When  the  same  number  of  heat  units  is  imparted  to  like 
weights  of  different  substances  their  temperatures  are  not 
raised  through  an  equal  number  of  degrees.  The  same 
amount  of  heat,  for  example,  which  will  raise  the  tempera- 
ture of  one  pound  of  water  from  32°  F.  to  33°  F.  will 
raise  a  pound  of  sand  from  32°  F.  to  37.23°  F.  For  some 
reason  more  work  must  be  done  on  water  than  on  the  sand 
to  secure  the  same  change  of  temperature,  but,  true  to  the 
law  of  the  conservation  of  energy,  when  the  water  again 
cools  down  it  gives  out  as  much  more  heat  in  doing  so  as 
was  required  to  produce  the  rise  in  temperature.  It  is 
this  fact  which  causes  large  bodies  of  water  to  make  the 
winters  of  adjacent  lands  warmer  and  the  summers  cooler. 
Soils  change  in  temperature  more  rapidly  than  would  be 
the  case  were  their  specific  heats  higher,  and  for  this  rea- 
son in  part  a  wet  soil  is  cooler  than  the  same  soil  when 
dryer. 

41.  Latent  Heat. — When  ice  at  32°  F.  has  heat  applied 
to  it  its  temperature  does  not  rise  so  long  as  there  is  still 
ice  to  melt,  the  whole  of  the  energy  given  to  it  being  con- 
sumed in  changing  the  solid  ice  into  liquid  water,  that  is, 


30  Introduction. 

in  doing  the  work  of  melting.  The  amount  of  heat  re- 
quired to  melt  one  pound  of  ice  is  142  units  when  ex- 
pressed in  round  numbers  ;  or  if  the  work  done  is  expressed 
in  foot-pounds  it  will  be 

142  X  778.3  =  110,518.6  foot-pounds 

and  the  time  required  for  one  horse  power  to  do  the  work 
would  be 

110,518.6 


When  crushed  ice  and  salt  are  mixed  in  the  ice-cream 
freezer  the  changing  of  the  two  solids  to  a  liquid  requires 
so  much  energy,  and  it  is  used  so  rapidly,  that  the  cream  is 
quickly  frozen,  its  molecular  motion  being  used  in  doing 
the  work. 

When  water  has  been  brought  to  the  boiling  tempera- 
ture it  ceases  to  become  warmer  so  long  as  boiling  contin- 
ues, all  of  the  heat  energy  entering  from  the  fire  being  re- 
quired to  do  the  work  of  changing  liquid  water  into  steam. 
The  amount  of  heat  required  to  change  one  pound  of  water 
at  212°  F.  into  steam  at  the  same  temperature  is  966.6 
hoat  units.  When  expressed  in  foot-pounds  it  becomes 

778.3X960.6  =  752,305 

p.nd  the  time  required  for  one  horse-power  to  do  this  work 
ia 

752,305        _00 

—  =22.8  minutes. 


60  X 


When  a  pound  of  water  at  32°  F.  becomes  ice  at  32°  F. 
there  reappears  as  heat  the  142  heat  units  which  were  re- 
quired to  melt  it,  and  so  too  when  one  pound  of  steam  con- 
denses into  water  there  reappears  966.6  heat  units.  Be- 
fore the  nature  of  these  changes  were  as  well  understood  as 


Latent  Heat  of  Water  and  Ice.  31 

they  now  arc,  it  was  supposed  that  the  heat  became  hidden 
or  latent  but  that  it  was  heat  still. 

42.  Measuring  the  Energy  Required  to  Melt  Ice. — This 
may  be  determined  approximately  by  taking  equal  weights 
of  water  at  212°  F  and  of  ice  at  32°  F.,  putting  the  two 
together  and  noting  the  temperature  at  the  moment  the  ico 
is  all  melted.  When  this  has  been  done  it  will  be  found 
that  the  combined  water  has  a  temperature  of  about  51°  F. 

If,  however,  equal  weights  of  water  at  32°  and  212°  are 
mixed  there  will  be  found  a  temperature  of 

212  +  32 
-2~ =122 

one  volume  of  water  having  lost   as  much   as   the  other 

gained. 

.     In  the  first  case,  however,  the  water  lost 

212  —  51  =  161 

while  the  ice  gained  only 

51  -  32  =  19. 

There  was  therefore  in  this  case  an  apparent  loss  of 
1G1  — 19  =  142° 

If  a  pound  of.  water  and  of  ice  had  been  taken  for  these  ex- 
periments it  is  plain  from  (38)  that  the  142  would  also 
represent  142  heat  units. 

43;  Measuring  the  Energy  Required  to  Evaporate  Water. 
" — If  a  pound  of  steam  at  212°  F.  be  condensed  within  5.37 
pounds  of  water  at  32°  F.  there  will  result  6.37  pounds  of 
water  having  a  temperature  very  close  to  212°  F.  The 
one  pound  of  steam  has  therefore  raised  the  temperature  of 
5.37  pounds  of  water  through 

2123—  32p=iSO° 


32  Introduction. 

212>  —  32°  =  180° 

without  having  its  temperature  materially  lowered.  The 
molecular  energy,  therefore,  which  the  one  pound  of  steam 
contained  was 

180  X  5.37  =  CC3.6  units. 

This  large  amount  of  energy  in  steam  explains  how  it  is 
able  to  do  so  much  work  when  acting  upon  the  engine  pis- 
ton and  why  a  burn  from  steam  may  be  so  much  more  se- 
vere than  that  from  boiling  water. 

44.  Evaporation  Cools  the  Soil. — We  have  seen  that  one 
pound  of  steam  in  condensing  into  water  generates  Ofifi.C 
heat  units,  and  that  the  reverse  statement  is  also  true, 
namely,  to  convert  a  pound  of  water  into  the  gaseous  state, 
under  the  mean  atmospheric  pressure,  requires  the  absorp- 
tion by  that  pound  of  9GG.G  heat  units.  When  one  pound 
of  water  disappears  from  a  cubic  foot  of  soil  by  evapora- 
tion, it  carries  with  it  heat  enough  to  lower  its  tempera- 
ture, if  saturated  sand,  32.8°  F. ;  and  if  saturated  clay 
loam,  28.8°  F. 

To  dry  saturated  sandy  soil  until  it  contains  one-half 
of  its  maximum  amount  of  water  requires  the  evaporation 
of  about  9.5  pounds  to  the  square  foot  of  soil  surface  when 
this  drying  extends  to  a  depth  of  one  foot,  while  the  simi- 
lar drying  of  clay  loam  requires  the  evaporation  of  11.5 
pounds,  and 

11.5-9.5  =  21bs. 

or  the  amount  of  evaporation  which  must  take  place  in  the 
clay  loam  to  bring  it  to  the  same  degree  of  dryness  as  the 
sandy  soil.  But  to  evaporate  two  pounds  of  water  re- 
quires 

9G6.6  X  2  =  1933.2  heat  units. 

and  this,  if  withdrawn  directly  from  a  cubic  foot  of  satur- 
ated clay  loam,  would  lower  its  temperature  57.6°  F. 
Here  is  one  of  the  chief  reasons  why  a  wet  soil  is  cold. 


Latent  Heat.  33 

Tlir.t  the  evaporation  of  water  from  a  body  does  lower  its 
temperature  may  be  easily  proved  by  covering  the  bulb  of 
a  thermometer  with  a  close  fitting  layer  of  dry  muslin,  not- 
ing the  temperature.  If  the  muslin  be  now  wet,  with 
water  having  the  temperature  noted,  and  the  thermomotcr 
rapidly  whirled  in  a  drying  atmosphere  its  temperature 
will  quickly  fall,  owing  to  the  withdrawal  of  heat  from  the 
bulb  by  the  evaporation  of  water  from  the  muslin. 

45.  Regulation  of  Animal  Temperatures. — All  of  our  do- 
mestic animals  require  the  internal  temperature  of  their 
bodies  to  be  maintained  constantly  at  a  point  varying  only 
a  little  from  100°  F.,  and  this  necessity  requires  provi- 
sions both  for  heating  the  body  and  cooling  it.     The  cool- 
ing of  the  body  is  accomplished  by  the  evaporation  of  per- 
spiration from  the  skin,  and  the  amount  of  perspiration  is 
under  the  control  of  the  nervous  system.     When  the  tem- 
perature becomes  too  high,  because  of  increased  action  on 
the  part  cf  the  animal,  or  in  consequence  of  a  high  ex- 
ternal  temperature,  the  sweat   glands    are    stimulated  to 
greater  action  and  water  is  poured  out  upon  the  evaporat- 
ing surfaces  and  the  surplus  heat  is  rapidly  carried  away ; 
each  pound  evaporated  by  heat  from  the  animal  withdraw- 
ing about  966. 6  heat  units. 

46.  Bad  Effects  of  Cold  Rains  and  Wet  Snows  on  Domestic 
Animals. — When  cattle,  horses  and  sheep  are  left  out  in  the 
cold  rains  of  our  climate  the  evaporation  of  the  largo 
amount  of  water  which  lodges  upon  the  bodies,  and  espe- 
cially in  the  long  wool  of  sheep,  creates  a  great  demand 
upon  the  animab  to  evaporate  this  water.     The  theoretical 
fuel  value  of  one  pound  of  beef  fat  is  16,331  heat  units, 
and  that  of  average  milk  is  1,148  heat  units.     A  pound  of 
beef  fat  may  therefore  evaporate 

16, 331 

„„(>  R  =  16.8  Ibs.  of  water 
9C6.6 

and  a  pound  of  average  cow's  milk 

1118 
',„.„  ,.  =  1.13  103.  of  water 


34  Introduction. 

On  this  basis,  if  a  cow  evaporates  from  her  body  four 
pounds  of  rain  she  must  expend  the  equivalent  of  the  solids 
of  3.39  pounds  of  milk. 

A  wet  snow-storm  is  often  worse  for  animals  to  be  out 
in  than  a  rain-storm,  because  in  this  case  the  snow  requires 
melting  as  well  as  evaporating,  and  the  number  of  heat 
units  per  pound  of  snow  is 

142.  C5  +  906.  6  =  1109.25  heat  units, 

and  the  heat  value  of  a  pound  of  milk  is  barely  sufficient 
to  melt  and  evaporate  a  pound  of  snow. 

47.  Cooling  Milk  with  Ice  and  Cold  Water.  —  If  it  is  de- 
sired to  cool  one  hundred  pounds  of  milk  from  80°  F. 
down  to  40°  F.  it  is  practically  impossible  to  do  so  with 
water  in  the  summer  season  in  Wisconsin.  It  is  difficult 
even  to  cool  it  as  low  as  48°  F.  for  most  of  the  well  and 
spring  water  has  a  temperature  above  45°  F.  and  much 
of  it  is.  above  50°  F.  If  lower  temperatures  than  48°  F. 
are  desired  during  the  warm  season  some  other  means 
must  be  resorted  to.  Since  it  requires  142  heat  units  to 
melt  a  pound  of  ice,  one  pound  is  capable  of  cooling  from 
80°  to  40°  F. 

3.751bs.  of  milk, 


supposing  the  specific  heat  of  milk  to  be  the  same  as  that 
of  water,  which  is  not  quite  true.  To  cool  100  pound?  of 
milk  from  80°  F.  to  40  F.  will  require,  therefore,  about 


100 

-=26  1    Ibs.  of  ice, 


3.75 

supposing  it  to  be  used  wholly  in  cooling  the  milk. 

If  the  water  has  a  temperature  above  40°  F.  before  the 
milk  and  ice  are  placed  in  it,  there  will  be  required  enough 
more  ice  to  cool  the  water  down  to  the  temperature  desired 
for  the  milk. 

The  greatest  economy  in  the  use  of  ice  will  be  secured, 
therefore,  when  the  creamer  contains  just  as  little  water 
as  will  cover  the  cans  and  give  the  needed  space  for  the  ice, 


Latent  Heat.  35 

and  when  the  walls  of  the  creamer  are  made  of  so  poor  a 
conductor  of  heat  as  to  admit  as  little  as  possible  from 
without. 

48.  Washing  with  Snow  or  Ice. — When  ice  or  snow  are 
used  in  winter  for  washing  purposes  there  is  a  large  loss 
of  heat  incurred  in  simply  melting  the  ice  and  raising  the 
temperature  of  the  water  from  32°  F.  up  to  45°  F.,  the 
temperature  it  may  have  in  any  well  protected  cistern. 
To  melt  a  pound  of  ice  and  raise  its  temperature  to  45°  F. 
will  require 

142  -f  13  =  155  heat  units, 

If  300  pounds  of  water  are  required  for  a  washing  then 
the  lost  heat  will  be 

300  X  155  =  46,500  heat  units. 

The  fuel  value  of  one  pound  of  water-free,  non-resinous 
wood,  such  as  oak  or  maple,  has  been  found  to  be  15,873 
heat  units;  that  of  ordinary  dry  wood,  not  sheltered,  con- 
taining 20  per  cent,  of  water,  is  12,272  heat  units.  At 
this  latter  value  it  will  require,  supposing  50  per  cent,  of 
the  fuel  value  to  be  utilized  in  melting  the  ice  and  heating 
the  water, 

2X46,500 

~^o  OTO    '  =  7.53  Iks.  of  wood 

I  -  .  —  (  — 

more  than  would  be  needed  to  do  the  same  washing  with 
water  at  45°  F.,  to  say  nothing  of  the  expense  of  getting 
the  snow  or  ice  and  the  unhealthfulness  of  handling  it. 

48a.  Burning  Green  or  Wet  Wood. — Whatever  water 
wood  or  other  fuel  may  contain  when  it  is  placed  in  the 
stove,  so  much  of  the  fuel  as  is  required  to  evaporate  this 
water  must  be  so  expended  and  is  prevented  from  doing 
work  outside  of  the  stove.  We  have  seen  (48)  that  when 
wood  contains  20  per  cent,  of  water  there  is  required 

15,873  —  12,272  =  3,601  heat  units 

per  pound  of  wood  to  evaporate  the  water  contained,  which 
is  22.7  per  cent,  of  the  total  value.  Wood,  after  being  in 


CO  Introduction. 

a  rain  of  several  days,  contains  more  water  than  this  and 
green  wood  much  more,  sometimes  as  high  as  50  per  cent., 
while  well  seasoned  sheltered  wood  may  contain  less  than 
half  that  amount. 

It  is  frequently  urged  that  when  some  green  or  wet  wood 
is  burned  with  that  which  is  dry  there  is  a  saving  of  fuel. 
There  is  some  truth  in  this,  especially  in  stoves  having  too 
strong  a  draft  and  too  direct  a  connection  with  the  chim- 
ney and  if  the  radiating  surface  is  small  or  poor.  The 
evaporation  of  the  water  prevents  so  high  a  temperature 
from  occurring  in  the  stove,  which  makes  the  draft  less 
strong,  and  this  gives  more  time  for  the  heat  to  escape 
from  the  stove  before  reaching  the  chimney,  and  hence 
less  is  lost  in  this  way.  Then  as  the  fire  burns  more 
slowly  there  is  not  the  overheating  of  the  stove,  at  times, 
which  may  occur  with  lack  of  care  when  very  dry  wood 
is  used,  and  a  considerable  saving  occurs  in  this  way. 
These  statements  apply  more  particularly  to  heating 
stoves  than  to  cooking  stoves.  Dry  wood  is  best  for  the 
kitchen  stove  under  most  circumstances,  the  slower  fire 
being  secured  when  needed  by  using  larger  sticks  and  by 
controlling  the  draft. 


SURFACE   TENSION,,  SOLUTION  AND  OSMOSIS. 

49.  Surface  Tension. — The  free  surface  of  any  liquid  be- 
haves much  as  though  it  were  covered  by  an  elastic  mem- 
brane and  it  is  this  surface  action  which  draws  the  rain- 
drop into  the  form  of  a  sphere  as  it  falls  through  the  air. 
It  is  surface  tension  that  causes  water  to  form  into  spheres 
on  a  dusty  floor,  on  a  hot  stove  or  on  cabbage  leaves.  The 
dewdrop  owes  its  shape  to  surface  tension,  and  it  is  this 
which  is  employed  to  mould  the  melted  lead  into  perfect 
spheres  as  it  falls  from  high  towers,  cooling  into  solid  shot 
before  reaching  the  bottom. 

The  cause  of  surface  tension  is  the  cohesive  attraction 
of  the  molecules  for  one  another.  This  attraction  extends 


Surface  Tension. 


action  °' 


throughout  the  liquid  and  is  very  strong;  but  only  the 
molecules   at  the  surface  show  | 
its  influence  because  it  is  only 
these    which    are    not    pulled 
evenly  in  all  directions  by  water 
molecules  on  every  side,   thus 
leaving  the  interior  ones  free  to 
move   in   any   direction,   while 
those  on  the  surface  are  only 
pulled  toward  the  sides  and  to- 
ward the  interior.     In  Fig.  3  is 
illustrated  one  method  of  show- ' 
ing  the  action  of  surface  ten- 
sion.     Here    the    dry    camel's       '  3'~~I 
hair  brush  at  the  left  shows  the 

individual  hairs  standing  apart,  and  when  the  brush  is 
placed  in  the  water  they  still  stand  apart,  but  Avhen  it  is 
removed,  as  shown  on  the  right,  the  whole  are  closely  com- 
pacted by  the  pull  of  the  surface  film. 

50.  Rise  of  Water  in  Capillary  Tubes. — It  is  surface  ten- 
sion which  causes  the  rise  of  water  in  capillary  tubes,  as 
represented  in  Fig.  4,  above  the  level  of  the  water  in  the 
open  vessel  in  which  they  are  placed,  when  the  water  wets 
the  glass  tube — that  is  when  the  attraction  of  the  glass  for 
the  water  is  stronger  than  the  attraction  of  the  water,  as 
explained  in  (191)  and  (192).  The 
rows  of  molecules  of  glass  just  above 
the  water  level  attract  and  lift  the 
water  closest  to  them  but,  as  these 
are  moved  upward,  they  draw  after 
themselves  more  water  also.  This 
attraction  is  felt  over  a  distance 
which  Quinke  estimates  at  not  far 
from  nnfffjnr  of  an  inch.  The  first 
lifting  of  the  water  by  the  glass 
brings  it  near  enough  to  other  glass 

FIG.  4.— Rise  of  water  m  cap-         ,  °    ,  ,  ,    , , 

iiiary  tubes,  molecules  next  above  and  the  water 

is  drawn  still  higher;  in  this  way 
3 


38  Introduction. 

the  column  rises  higher  and  higher  until  the  strength  of  the 
pull  is  balanced  by  the  weight  of  the  water  column  so 
lifted. 

51.  Evaporation. — Very   many   substances,    when   they 
have  a  free  surface  exposed,  change  in  weight  by  evapora- 
tion.    The  action  of  heat  causes  the  molecules  to  vibrate 
rapidly  and  by  colliding  with  one  another  near  the  free  sur- 
face some  are  thrown  out  by  the  force  and  direction  of  the 
blows.     It  is  in  this  way  that  clothes  dry  rapidly  on  a 
warm  day,  and  that  water  evaporates  from  the  surface  of 
the  soil,  from  the  leaves  of  plants  and  from  the  bodies  of 
animals.     Even  snow  and  ice  evaporate,  as  camphor  does, 
without  first  becoming  liquid,  but  the  process  and  the  cause 
are  the  same  as  the  evaporation  of  water,  namely,  rapid 
vibration  and  collision  at  the  surface  due  to  the  absorption 
of  heat  energy  from  outside. 

It  is  often  said  that  the  air  takes  up  the  moisture  and 
the  more  rapidly  the  dryer  it  is  or  the  stronger  the  wind 
blows.  The  air  itself  is  not  the  cause  of  the  more  rapid 
evaporation  observed,  neither  does  evaporation  stop  when 
the  air  becomes  saturated  with  moisture.  Evaporation 
may  be  even  more  rapid  in  a  vacuum  and  in  rarefied  air 
than  where  the  air  is  dense  and  the  pressure  heavy ;  and 
when  the  air  is  saturated  with  water  vapor  and  evaporation 
appears  to  stop,  it  may  be  going  on  just  as  rapidly,  only 
condensation  may  be  taking  place  at  the  same  rate,  that  is, 
just  as  many  molecules  of  water  return  from  the  space 
above  the  surface  as  leave  it  in  a  unit  of  time. 

52.  Solution  of  Solids. — The  solution  of  solids,  like  sugar 
or  salt  in  water,  is  not  fundamentally  different,  either  in 
cause  or  in  manner,  from  the  evaporation  of  water  or  of 
camphor  referred  to  in  (51),  and  is  due  to  the  absorption 
of  heat  from  without  which  causes  some  of  the  surface 
molecules  to  be  thrown  into  such  rapid  motion  that  the 
attractive  force  which  draws  them  toward  the  center  is  no 
longer  able  to  retain  them  in  place  and  they  are  thrown 
out. 


Solution  of  Solids.  39 

When  a  lump  of  salt  is  dropped  into  water  its  surface 
molecules  are  drawn  outward  by  the  surrounding  water  so 
that  the  effective  pull  upon  them  toward  the  center  is  made 
less  by  it.  It  is  therefore  easier  for  a  given  temperature 
to  throw  out  into  the  water  some  of  the  molecules  in  the 
surface  layer  of  the  salt.  Stated  in  another  way  the  water 
surrounding  the  salt  so  weakens  the  surface  tension  of  the 
solid  lump  of  salt  that  solution  takes  place  at  a  lower  tem- 
perature. 

53.  Influence  of  Temperature  on  Solution — Since  it  is  the 
absorption  of  heat  which  causes  solution  it  is  clear  that  the 
higher  the  temperature  the  more  rapid  will  the  solution  be. 

.It  is  even  true  that  any  solid  will  evaporate  or  dissolve  if 
only  it  is  given  a  high  enough  temperature,  provided  its 
molecules  are  not  decomposed  at  a  lower  temperature  than 
that,  which  is  required  to  overcome  the  force  of  cohesion 
which  makes  them  solid.  It  is  a  matter  of  common  ob- 
servation that  substances  dissolve  more  rapidly  in  warm 
than  in  cold  water  and  it  is  equally  true  that  the  soluble 
salts  in  the  soil  will  form  more  rapidly  when  the  soil  is 
warm  than  when  it  is  cold  and  it  is  because  of  this  fact,  in 
part,  that  crops  grow  better  under  the  higher  temperature. 

54.  A  Saturated  Solution. — When  conditions  are  favor- 
able for  the  solution  of  a  solid  in  water  there  comes  a  time 
when  there  is  no  increase  in  the  concentration  of  the  solu- 
tion.    A  condition  is  reached  which  is  analogous  to  the 
air  saturated  with  moisture,  when  as  many  molecules  pass 
from  the  solution  and  become  fixed  upon  the  face  of  the 
solid  as  are  thrown  by  heat  from  the  face  of  the  solid  into 
the  solution.     When  a  solution  reaches  this  condition  it  is 
said  to  be  saturated. 

In  the  case  of  the  soil  water,  where  the  roots  of  plants 
are  brought  in  contact  with  it,  if  the  roots  are  removing 
the  materials  which  are  dissolved,  their  action  hastens  the 
rate  of  solution,  for  they  prevent  it  from  becoming  satur- 
ated and  thus  prevent  the  return  to  the  soil  grains  of  par- 
ticles once  removed. 


40 


Introduction. 


55.  Diffusion — When  water  has  evaporated  into  the  air ; 
when  a  salt  has  dissolved  in  water,  there  is  a  tendency  for 
these  separated  molecules  to  travel  in  any  and  all  direc- 
tions until  the  whole  body  of  the  liquid  in  which  the  solu- 
tion is  taking  place  contains  the  same  number  of  the  dis- 
solved molocules  per  cubic  inch.  A  lump  of  sugar  placed 
in  the  bottom  of  a  cup  of  tea  dissolves  in  time  and  be- 
comes scattered  uniformly  through  the  whole  mass,  making 
all  parts  equally  sweet.  This  scattering  of  molecules  is 
called  diffusion  and  the  rate  varies  with  the  temperature 
and  the  individual  velocities  of  the  molecules  dissolved. 


B  A 

Fro.  5.— Illustrating  the  difference  in  Iho  rate  of  diffusion  in  soil  and  ia  liquids 

The  rate  of  diffusion  of  salts  in  a  vessel  of  water 
is  much  more  rapid  at  the  same  temperature  than  it  could 
be  if  the  water  were  filled  with  sand.  This  will  be  under- 
stood from  a  study  of  Fig.  5,  where  A  is  supposed  to  be 
a  place  from  which  salts  are  diffusing  through  the  water 
surrounding  a  set  of  soil  grains,  while  B  is  a  correspond- 
ing point  from  which  diffusion  is  taking  place  in  direc- 
tions indicated  by  the  arrows  of  that  figure.  Where  the 
diffusion  must  take  place  through  the  films  surrounding 
the  soil  moisture  not  only  is  there  less  water  to  travel  in 
but  the  course  of  the  molecules  must  be  many  times  ar- 
rested by  the  soil  grains  themselves. 

56.  Gaseous  Pressure — The  pressure  which  is  exerted 


Osmosis.  41 

by  gaseous  bodies  like  air  or  steam,  upon  the  walls  of 
confining'  chambers  or  vessels,  is  due  to  the  combined 
energy  of  the  blows  of  the  molecules  against  these  walls. 
The  greater  the  number  of  molecules  in  a  given  space 
and  the  more  rapidly  they  move  the  greater  is  the  pressure 
they  exert.  If  the  temperature  of  a  gas  is  increased, 
leaving  the  volume  the  same,  the  pressure  is  increased  in 
the  same  ratio,  because  the  velocity  with  which  the  mole- 
cules are  moving  is  increased.  So,  too,  if  the  number  of 
molecules  of  a  given  gas  in  a  given  space  is  increased  the 
pressure  is  increased  in  a  like  ratio,  if  the  temperature 
remains  the  same,  because  then  there  are  more  molecules 
to  strike  a  unit  area  in  a  given  time. 

To  double  the  pressure  on  a  gas  will  reduce  its  volume 
one-half  and  to  double  the  volume  of  a  gas  will  reduce  its 
pressure  one-half.  So,  too,  will  doubling  the  absolute  tem- 
perature of  a  gas  double  its  pressure  if  it  is  not  allowed  to 
expand.  It  is  on  these  accounts  that  the  higher  the  steam 
pressure  in  a  boiler  the  hotter  it  is  and  the  more  work  it  is 
capable  of  doing. 

57.  Osmosis. — Abbe  Nollet,  who  lived  between  1700  and 
1770,  appears  to  have  been  the  first  to  record  that,  if 
a  glass  vessel  be  filled  with  wine  and  covered  with  a 
bladder  and  then  immersed  in  water,  the  contents  of  the 
vessel  would  increase  and  sometimes  to  such  an  extent 
as  to  rupture  the  membrane.  Such  a  phenomenon  has 
been  named  osmosis,  and  there  are  many  familiar  phe- 
nomena of  every  day  experience  which  are  of  the  same 
nature. 

When  dry  beans,  peas  or  grain  of  any  kind  are  put  into 
water  they  swell,  increasing  in  volume  as  the  wine  in 
Collet's  covered  dish  did  when  placed  in  water.  So,  too, 
if  dried  raisins,  prunes  or  apples  are  placed  in  water 
they  increase  in  size,  thus  exhibiting  the  process  of  osmosis. 

On  the  other  hand  if  fresh  fruit  of  almost  any  kind 
ia  placed  in  a  strong  solution  of  sugar  it  at  once  begins 
to  shrivel  and  decrease  in  size;  this  again  is  due  to  osmosis, 


4:2  Introduction. 

the  juices  being  forced  from  the  fruit  by  the  pressure 
of  the  dissolved  sugar  as  will  be  explained  in  the  next 
section. 

58.  Osmotic  Pressure. — The  power  which  causes  the  swell- 
ing of  the  dried  grains  and  fruits  and  that  which  causes 
the  shrinkage  of  the  fresh  fruit,  in  the  cases  cited  in  (57), 
is  known  as  osmotic  pressure  and  is  caused  in  fundamental- 
ly the  same  manner  as  that  of  gaseous  or  steam  pressure, 
but  in  this  case  by  molecules  of  substances  in  solution 
moving  in  the  same  manner  as  the  molecules  of  gas  move 
when  developing  gaseous  pressure. 

59.  Conditions  \Jnder  "Which  Osmotic  Pressure  Becomes 
Manifest. — In  order  that  the  molecules  of  a  dissolved  sub- 
stance may  exert  pressure  analogous  to  gases  they  must 
be  dilute  solutions,  so  that  the  individual  molecules  of 
the  kind  manifesting  the  pressure  are  too  far  from  one 
another  to  be  influenced    by  their  individual  attractions; 
besides  this,  in  order  that  the  pressure  may  become  mani- 
fest, the  dissolving  substance  and  the  substance  dissolved 
must  be  separated  by  a  membrane  through  which  the  mole- 
cules of  one  of  the  fluids  pass  more  readily  than  the  other, 
as  represented  in  Fig.  G. 


FIG.  6. — lllustrat  ing  the  principle  of  osmotic  pressure. 


Osmosis.  43 

The  diagram  on  the  left  may  represent  a  raisin,  dry 
bean  or  other  dry  seed  placed  in  water,  the  upper  circle 
showing  the  conditions  just  as  placed  in  the  water,  and 
the  larger  one  after  the  water  has  diffused  through  the 
wall,  dissolving  the  substances  on  the  inside,  which  pro- 
duce the  osmotic  pressure.  In  this  diagram  it  is  supposed 
that  the  surrounding  membrane  is  porous  enough  to  let 
the  molecules  of  water  pass  readily  through  by  the  or- 
dinary laws  of  diffusion,  but  the  molecules  of  the  sub- 
stance inside,  which  is  dissolved  by  the  entering  water, 
are  too  large  to  be  able  to  pass  out  into  the  water  by 
diffusion,  and  the  result  is  they  simply  strike  against 
the  membrane,  distending  it  in  exactly  the  same  way  that 
the  molecules  of  air  in  a  rubber  ball  or  rubber  bicycle 
tire  distend  that. 

In  the  diagram  on  the  right  in  Fig.  6,  the  reverse  con- 
ditions are  represented.  A  green  or  fresh  fruit  is  sup- 
posed to  be  placed  in  a  solution  of  sugar,  whose  molecules 
are  too  large  to  readily  pass  into  the  fruit  through  its 
wall,  while  the  contained  sap  of  the  fruit  readily  diffuses 
outward  into  the  sweetened  water.  Under  these  con- 
ditions the  molecules  of  sugar,  striking  against  the  fruit 
on  all  sides  at  once,  develop  so  much  pressure  that  the 
juices  of  the  berry  are  squeezed  out  of  it  as  water  might 
be  forced  out  of  a  sponge,  and  its  volume  is  reduced  from 
the  large  size  in  the  upper  part  of  the  diagram  to  the 
smaller  one  in  the  lower  portion. 

60.  Measurement  of  Osmotic  Pressure. — It  was  a  long 
time  after  the  discovery  of  osmotic  pressure  before  satis- 
factory means  for  measuring  its  full  intensity  were  de- 
vised. The  parchment  and  animal  or  vegetable  mem- 
branes which  were  first  used  in  such  studies  were  either 
not  sufficiently  impervious  to  the  pressure  producing  mole- 
cules or  else  their  strength  was  not  great  enough  to  allow 
the  full  measure  of  pressure  to  develop  and  the  result  was 
the  early  experiments  failed  to  show  how  powerful  osmotic 
pressure  may  become  when  the  conditions  are  all  favor- 
able. 


44 


Introduction. 


Tranbe  discovered  the  possibility  of  producing  mem- 
branes by  chemical  precipitation,  at  the  plane  of  contact 
between  two  solutions,  which  could  be  used  instead  of  or- 
ganic membranes  to  study  osmotic  pressure,  and  later 
Pfeffer  devised  the  apparatus  represented  in  Fig.  7,  with 


FIG.  7. — Pfeffer's  apparatus  for  measuring  osmotic  pressure. 

which  he  was  able  to  measure  osmotic  pressures  of  very 
high  intensity  and  with  a  fair  degree  of  accuracy.  He  used 
a  porous  porcelain  cell  Z,  with  three  glass  pieces,  t,  v,  r, 
put  together  with  sealing  wax  in  the  manner  represented 
in  section  in  the  left  of  the  figure,  where  the  method  and 
arrangements  for  measuring  the  pressure  are  also  shown 
at  a,  m.  The  complete  apparatus,  in  working  order,  is 
represented  at  the  right  in  the  same  figure. 


Osmosis. 


45 


To  secure  the  manifestation  of  osmotic  pressure  with 
this  apparatus  there  is  developed,  on  the  inner  wall  of  the 
porous  porcelain  cell,  a  precipitation  membrane  which  is 
impervious  to  the  solution  whose  pressure  is  to  be 
measured  but  which  is  readily  permeable  by  water,  placed 
in  the  outer  vessel.  The  function  of  the  porous  cell  is 
to  act  as  a  strong  framework  capable  of  permitting  the 
precipitation  membrane  to  withstand  the  pressure  de- 
veloped without  a  sensible  increase  in  the  volume  of  the 
cell  taking  place.  When  the  pressure-producing  fluid  is 
placed  on  the  inside  and  the  apparatus  is  placed  in  water 
the  case  becomes  analogous  to  the  left  diagram  of  Fig.  6, 
except  that  the  wall  is  now  incapable  of  expansion  and  the 
pressure  becomes  manifest  through  the  rise  of  mercury  in 
the  pressure  gage.* 

61.  Osmotic  Pressure  of  Cane  Sugar. — Pfeffer,  working 
with  his  apparatus  and  different  strengths  of  cane  sugar 
in  solution  on  the  inside,  was  able  to  show  that  pressures 
were  developed  having  the  intensities  indicated  in  the  table 
below : 

Table  shoiving  osmotic  pressure  of  solutions  of  cane  sugar  of 
different  degrees  of  concentration. 


Strength  of  solution. 

Pressure  in  m.m. 
of  mercury. 

Pressure  per 
sq.  inch. 

Height  of  colrmn 
of  water  susti  iued, 
in  feet. 

535 

Ibs. 
10  36 

23.9 

2  per  cent  

1,016 

19  68 

45.4 

2.74  per  cent  

1,518 

29.41 

67.8 

4  per  cent  

2.0S2 

40  34 

93.0 

6  per  cent  .. 

3  075 

59  57 

137.4 

From  this  table  it  appears  that  Pfeffer  was  able  to 
secure  pressures  ranging  from  about  10  to  60  pounds  per 
square  inch,  or  enough  to  sustain  a  column  of  water  from 
24  to  137  feet  high. 

*  Detailed  descriptions  of  the  method  of  forming  the  membrane 
and  setting  up  the  apparatus  can  be  found  in  Gray's  Botanical  Text 
Book,  6th  Ed.,  Vol.  II,  p.  5:27,  and  in  Jones'  The  Modern  Theory  cf 
Solutions,  p.  3. 


4:6  Introduction. 

Using  a  3.3  per  cent,  solution  of  potassium  nitrate  in  his 
apparatus  Pfeffer  secured  a  pressure  of  nearly  85  pounds 
per  square  inch  or  enough  to  sustain  a  column  of  water 
195  feet  high.  This  force  has  been  looked  upon  as  the 
cause  of  the  movement  of  sap  in  plants  and  it  was  a  search 
for  a  cause  for  this  movement  which  led  Pfeffer  to  make 
the  observations  here  referred  to. 

62.  Influence  of  Temperature  on  Osmotic  Pressure. — 
Pfeffer  extended  his  observations  so  as  to  measure  the 
influence  of  different  temperatures  on  the  osmotic  pressure 
of  the  same  solution  in  the  same  piece  of  apparatus  and 
some  of  the  results  he  obtained  are  given  in  the  next 
table. 

*  Table  showing  the  influence  of  temperature  on  the  in- 
tensity of  osmotic  pressure. 

1  With  temp.  14.2°C.  pressure=51  c.  m.  but  with  temp.  32°C.pressure=  54.4  c.  m. 

2  "        "       6.8  "      —50.5          "       "        "      13.7  "      =  52.5     " 

3  "     •  "     15.5  "      =52.  "       "        "      36.0  "      =56.7     " 

In  order  to  understand  the  relation  of  osmotic  pressure 
to  temperature  it  is  necessary  to  state  them  in  terms  of 
degrees  above  absolute  zero  (32)  rather  than  above  the 
temperature  at  which  water  freezes.  When  the  results  are 
stated  with  reference  to  the  absolute  zero  of  temperature 
they  stand  as  below: 

1  With  temp.  287.92°C  pressure=51  c.  m.  but  with  temp.  305.72°C  pressure- 54.4  c.m. 

2  "        "    280.52  "        =50.5          "      <'       "       287.42  "        =52.5     " 

3  "        "    289.22  «'       =52.  "      "      "       309.92  "        =56.7    " 

These  observations  are  in  harmony  with  others  regard- 
ing plant  growth  which  show  that  a  low  soil  temperature 
may  cause  plants  to  wilt  even  in  the  night  when  evapora- 
tion from  the  leaf  surface  is  small,  while  a  high  soil  tem- 
perature may  increase  the  root  pressure  to  such  an  extent 
as  to  cause  drops  of  water  to  form  at  the  tips  of  leaves  in 
a  bright  day. 

62a.  Osmosis  and  Diffusion  in  Plant  Feeding. — If  in  a 
plant  cell  water  is  being  used  in  the  production  of  some 
substance  such  as  starch,  sugar  or  cellulose,  the  water 


Osmosis.  47 

molecules  will  be  removed  from  solution  and  prevented 
from  exercising  pressure,  thus  causing  a  reduction  of  the 
osmotic  water  pressure  in  that  cell;  this  will  permit  more 
water  from  the  adjacent  cells  to  be  driven  in  to  make  good 
the  loss. 

So,  too,  if  water  is  being  lost  by  evaporation  from  the 
leaves,  this  loss  will  result  in  a  reduced  osmotic  water 
pressure  in  the  leaf  cells  which  will  permit  the  heavier 
pressure  in  the  cells  extending  backward  toward  and  to 
the  root  hair  in  the  soil  to  force  more  water  onward 
toward  the  leaves  and  thus  maintain  the  flow  of  water  by 
powerful  osmotic  pressure  toward  the  leaves  as  long  as 
evaporation  continues. 

When  nourishment  is  being  stored  in  the  seed  the  sub- 
stances in  solution  in  the  sap  are  being  taken  out  and 
laid  down  in  solid  form,  thus  tending  to  maintain  at  that 
place  a  reduced  osmotic  pressure  which  permits  the  sub- 
stance of  that  sort  to  be  forced  continually  toward  the 
place  where  the  formation  is  going  on.  In  this  way  the 
starch  and  other  products  are  supposed  to  be  brought  from 
the  leaves  and  stems  to  the  seeds  or  places  in  stems,  like 
the  potato,  where  food  products  are.  being  stored. 

In  the  gathering  of  nitrogen  from  the  nitrates  in  the 
soil  water,  too,  the  process  would  be  the  same.  Wherever 
the  nitrate  is  being  transformed  there  its  osmotic  pres- 
sure would  be  falling  and  this  permits  more  to  be  forced 
to  the  same  point. 

The  so-called  selective  power  of  plants,  whereby  they 
obtain  those  substances  dissolved  in  the  soil  water  which 
they  need,  is  thus  explained.  It  should  be  understood 
that  unless  the  mole-cules  of  a  substance  in  solution  are 
too  large  to  pass  from  cell  to  cell  through  the  walls  these 
substances  will  do  so  until  the  solution  inside  the  plant 
has  a  strength  equal  to  that  outside,  but  if  this  substance 
chances  to  be  one  which  the  plant  does  not  use  there  will 
be  no  further  concentration  of  that  substance  in  the  plant 
unless  it  be  at  places  where  evaporation  is  taking  place. 

If  a  poisonous  principle  exists    in   the   soil   water   os- 


48  Introduction. 

motic  pressure  will  tend  to  force  this  substance  into  the 
plant  tissues  and  the  plant  is  helpless  to  prevent  this  en- 
trance. 

63.  Dissociation  of  Salts  in  Solution. — There  is  a  large 
class  of  substances  which,  when  they  go  into  solution  in 
water,  increase  its  electrical  conductivity.  It  is  also  true 
that  the  osmotic  pressure  which  they  may  develop  is 
greater  than  can  be  explained  on  the  basis  of  the  number 
of  molecules  which  were  contained  in  the  salt  before  its 
solution  occurred.  To  account  for  both  the  greater  electric 
conductivity  and  the  higher  osmotic  pressure  in  such  cases 
it  has  been  assumed  that,  at  the  time  of  solution,  more 
or  less  of  the  molecules  dissolved  separate  into  two  groups, 
each  of  which  may  take  part  in  developing  osmotic  press- 
ure, making  it  greater  than  it  could  otherwise  be. 

When  a  very  dilute  solution  of  potassium  nitrate,  for  ex- 
ample, is  made,  it  is  supposed  that  the  molecules  are 
broken  into  two  groups,  each  of  which  may  absorb  heat 
energy  and  so  strike  a  greater  number  of  blows  per  unit 
of  time  against  the  confining  membrane,  and  in  this  way 
produce  a  higher  pressure.  The  two  ions,  as  they  are 
called,  act  like  two  hammers  and  each  is  able  to  absorb 
and  deliver  more  energy  when  moving  separately  than 
when  combined  as  a  single  but  heavier  hammer. 


PHYSICS  OF  THE  SOIL, 


CHAPTER  I. 

NATURE,  ORIGIN  AND  WASTE  OF  SOIL. 

64.  Nature  of  the  Soil.— The  great  bulk  of  most  soils  is 
made  up  of  small  fragments  of  rock  of  various  kinds,  but 
nearly    always    there    is    associated    with    these    varying 
amounts  of  organic  matter  derived  from  the  breaking  down 
of  plant  and  animal  tissue. 

On  the  surface  of  the  soil  grains,  too,  there  is  always  ad- 
hering more  or  less  of  substances  which  have  been  dis- 
solved in  the  soil-water  but  which  have  been  deposited  again 
when  the  water  was  evaporated. 

In  most  soils,  but  chiefly  in  the  clayey  types,  there  oc- 
curs some  aluminium  silicate  having  water  combined  with 
it,  which  is  regarded  as  giving  to  them  their  sticky,  plastic 
quality  when  wet.  The  amount  of  this  material  in  a  good 
soil  is  always  small,  seldom  reaching  more  than  1.5  per 
cent.,  but  the  particles  are  so  extremely  minute  that  very 
little  by  weight  has  a  marked  effect  upon  its  character. 

65.  Soils  and  Sub-soils. — In  climates  where  the  rainfall  is 
sufficient  for  large  crops  it  is  common  to  speak  of  the  sur- 
face few  inches  of  rock  fragments  as  the  soil  while  that 
below  is  known  as  the  sub-soil.       The  fundamental  reason 
for  making  this  distinction  is  found  in  the  fact  that  the 
latter  is  less  productive  than  the  surface  soil.     So  general 
is  this  difference  in  fertility  that  the  term  "dead-furrow" 
has  been  universally  applied  to  the  finishing  of  a  land 
in  plowing  where  the  two  furrows  are  thrown  in  opposite 


50  Physics  of  the  Soil. 

directions,  leaving  the  sub-soil  exposed,  and  where  crops 
are  always  smaller.  On  the  other  hand,  where  two  fur- 
rows are  thrown  together  to  form  the  "back-furrow"  and 
the  depth  of  soil  increased  crops  are  notably  more  vigorous. 

We  do  not  yet  know  just  why  a  sub-soil ,  when  exposed 
to  the  surface  is  less  productive  than  the  true  soil,  but  the 
difference  seems  in  some  way  to  be  associated  with  the 
larger  per  cent,  of  the  extremely  minute  particles  which 
sub-soils  contain. 

In  arid  regions  where  the  rainfall  is  not  sufficient  for 
crop  production  it  seldom  occurs  that  the  deeper  soil  is 
markedly  different  in  productiveness  from  that  at  the  sur- 
face. Soil  taken  from  the  bottom  of  cellars  and  even  from 
depths  as  great  as  30  feet  is  found  quite  as  productive 
when  placed  upon  the  surface  as  the  top  soil.  So  gener- 
ally true  is  this  that  when  it  is  desirable  to  level  fields  for 
purposes  of  irrigation  in  arid  climates  the  soil  from  the 
higher  places  may  be  scraped  to  the  lower  levels  without 
fear  of  lessening  the  productiveness  of  the  fields. 

66.  Uses  of  Soil. — In  the  agricultural  sense  the  most  im- 
portant use  of  soil  is  to  act  as  a  storehouse  of  moisture  for 
the  use  of  plants;  and  the  productiveness  of  any  soil  is  in 
a  very  large  degree  determined  by  the  amount  it  can  hold, 
by  the  manner  in  which  it  is  held  and  by  the  readiness  and 
completeness  with  which  the  plant  growing  in  it  is  able  to 
withdraw  that  water  for  its  use  as  needed. 

In  the  second  place,  the  soil  is  a  storehouse  from  which 
plants  derive  the  ash  ingredients  of  their  food,  the  lime, 
the  potash,  phosphoric  acid  and  other  materials  of  this  class, 
all  of  which  are  derived  from  the  slow  decay  and  solution 
of  the  soil  grains. 

Besides  these  the  soil  is  a  laboratory  in  which  a  great 
variety  of  microscopic  forms  of  life  are  at  work  during 
the  warm  portions  of  the  year,  breaking  down  the  dead 
organic  matter  of  the  soil,  converting  it  into  nitric  acid 
and  other  forms  available  to  higher  plants,  and  the  student 
must  never  forget  that  the  magnitude  of  the  crop  taken 


Formation  of  Soil.  51 

from  the  field  is  always  in  proportion  to  the  size  of  the 
crop  developed  by  the  micro-organisms  in  the  soil. 

Then  again;  the  soil  is  a  medium  in  which  plants  may 
place  their  roots  in  such  a  manner  as  to  enable  them  to 
stand  erect  in  the  open  sunshine  and  moving  air  currents 
above. 

Finally,  the  soil  is  a  means  whereby  the  sunshine  is 
changed  into  forms  of  energy  available  to  the  needs  of  soil 
organisms  and  the  roots  of  plants  and  without  which  this 
life  could  not  exist ;  for  all  of  its  movements  must  originate 
primarily  from  the  sunshine  altered  in  the  soil  or  in  the  tis- 
sues of  the  plant  above  the  soil. 

67.  Formation  of  Soil — There  are  many  agencies  at  work 
in  the  formation  of  soils  and  the  processes  of  soil  growth 
are  in  continuous  operation  day  and  night,  winter  and  sum- 
mer. Since  all  soil  material  originates  from  the  breaking 
dowyn  of  the  various  rock  structures  which  make  up  the 
earth's  surface  all  of  the  agencies  which  are  operative  in 
rock  destruction  may  also  contribute  to  soil  formation. 

68.  Influence  of  Hock  Texture  on  Soil  Formation. — Nearly 
all  kinds  of  rock  are  made  up  of  fragments  or  crystals  of 
various  sizes  and  shapes  and  these  are  held  together  by  in- 
terlocking, by  some  cementing  material,  or  else  by  direct 
cohesion  when  extreme  pressure  has  brought  the  grains 
close  enough  together  to  make  this  possible.  It  is  seldom 
true,  however,  that  the  structure  is  so  close  or  the  cement- 
ing so  complete  as  to  make  the  rock  impervious  to  water 
and  the  closest  granite  or  the  finest  marble  may  absorb 
as  much  as  .1  to  .4  of  a  pound  of  water  to  100  pounds  of 
rock.  If  this  water  is  changing  it  will  dissolve  away  the 
cementing  materials  and  the  faces  of  the  crystals  them- 
selves, making  the  rock  still  more  open  and  the  grains  may 
even  fall  apart  as  is  frequently  observed  in  those  cases 
known  as  "rotten  stones." 

The  water  may  freeze  in  the  stone  and  by  its  expansion 
cause  it  to  crumble.  Or  again,  when  the  sun  shines  on 


52 


Physics  of  the  Soil. 


rocks  made  up  of  minerals  of  different  kinds  the  crystal? 
do  not  all  expand  at  the  same  rate  and  this  unequal  expan- 
sion and  contraction  tends  to  loosen  crystals  and  fragments, 
breaking  the  rock  down,  and  thus  form  soil. 


FlQ.  8. —  Section  of  limestone  hill  showing  rock  changing  to  soil. 
(After  Chamberlin.) 

69.  Formation  of  Soil  From  Limestone — If  one  will  visit 
any  limestone  quarry  where  the  soil  and  rock  are  exposed 
in  section  as  represented  in  Figs.  8  and  9  it  will  be 
clearly  seen  how  the  rock  is  slowly  converted  into  soil.  In 
such  cases  as  these,  the  water  containing  carbonic  or  other 
acids  dissolves  away  the  lime  and  magnesia,  leaving  the 
more  insoluble  portions  of  the  lime  rock  to  form  the  soil 
mantle  which  is  left.  These  more  insoluble  portions  are 
usually  clay  and  very  fine  sand  so  that  soils  formed  in  this 
way  are  oftenest  clayey  soils,  sometimes  containing  even 
less  lime  than  other  soils  not  derived  from  limestone. 


FIG.  9. —  Section  of  flat  limestone  surface  showing  rock    changing    to    soil. 
(After  Chamberlin.) 

The  mantle  of  soil  seen  above  gravel  beds  in  railroad 
cuts  and  \vhere  hills  have  been  graded  down  on  wagon  roads 
has  usually  most  of  it  originated  from  the  decomposition 
of  the  gravel  in  place  in  the  same  manner  as  a  soil  from 
the  limestone  itself.  So,  too,  in  countries  where  granite 
and  other  crystalline  rocks  lie  beneath  the  soil,  these  have 


Formation  of  Soil. 


53 


been  broken  down  and  - 
the   over-lying  soil   de- 
rived from  them. 

70.  Influence  of  Rock 
Fissures. — An  examina- 
tion of  almost  any  quar- 
ry where  considerable 
surfaces  are  exposed  re- 
veals the  presence  of 
systems  of  fissures  which 
divide  the  stone  layers 
into  blocks  of  various 
sizes  and  at  the  same 
time  provide  easy  ave- 
nues for  the  entrance  of 
surface  waters.  These 
features  are  shown 

clearly   in  FlgS.    10,    11,  FIG   10.— Fort  Danger,  Wis.,  showing  rock  fls- 
19,      iiirl      13       nnrl      intn        fcures    which     lead    to    rock    destruction. 
L0>  (After  Chamberliu.) 

them  the  roots  of  trees 

sometimes  make  their 
way  where  by  expansion, 
due  to  growth,  such  strong 
pressures  are  developed 
as  sometimes  to  throw 
down  large  blocks  of 
stone.  Then  again,  in 
cold  climates  these  fis- 
sures may  become  filled 
with  water  which,  when 
freezing,  overturns  and 
throws  down  many  frag- 
ments, thus  hastening 
their  passage  into  soil. 

71.  Soil  Removal. — It 
follows  from  what  has 
been  said  that  the  same 
processes  which  result  in 

FIG.  11.  -Bee  Bluff,  Wis.,  showing  rock  fis.=nre?  *    .,     _  .  , 

which  lead    to    rock  destruction.      (After  SOll   lOrmatlOn   niUSt   alSO 

chamberiin.)  contribute  to  its  destruc- 

4 


54  Physics  of  the  Soil. 

tion  in  one  place  or  re- 
moval to  another.  All 
are  familiar  with  the 
creeping  of  soils  from 
the  brows  of  steep  hill- 
sides toward  their  bases 
and  out  upon  the  more 
level  plains  which 
stretch  away  from  them. 
These  downward  move- 
ments are  caused  by  sev- 
eral agencies:  (1)  The 
beating  of  falling  rain- 
drops and  the  carrying 
power  of  the  streamlets 
which  form  as  these 
gather  together ;  (  2  )  the 
expansion  and  contrac- 
tion of  the  soil  due  to 
the  alternate  wetting 

and  drying,  there  being  FIG.  12.— Giant's  Castle,  near  Camp  Douplas, 
•,  .  ,  Wis.,  showing  cliff's  of  rock  crumbling  into 

less  resistance  to  expan-        soil.    (After  Cbamberlin.) 

sion  downward  than  upward  against  gravity.  These 
movements  are  analogous  to  those  of  the  steel  rails  of 
the  railroad  which  tend  to  creep  down  grade  under  the 
influence  of  changing  temperature,  which  causes  them  to 
first  lengthen  and  push  down  hill  and  then  shorten  and 
again  draw  downward  because  of  less  resistance  in  that 
direction.  (3)  Then,  again,  every  disturbance  of  the 
soil  produced  by  animals  burrowing  or  walking  up  or  down 
the  hillside,  tends  usually  to  work  the  soil  from  higher  to 
lower  levels.  Even  the  action  of  the  wind  is  on  the  whole 
downward. 

72.  Soils  Produced  by  Running  Water. — Rivers  and 
streams  are  continually  at  work  at  this  double  process  of 
soil  building  and  soil  removal.  When  one  watches  the  bed 
of  a  stream  as  the  water  ripples  over  the  uneven  surface 


Formation  of  Soil. 


55 


it  is  easy  to  note  how  rapidly  soil  and  sand  grains  are  be- 
ing rolled  and  tumbled  along  the  bottom.  If  it  is  desired 
to  measure  this  rate  of  movement  a  shallow  pan  or  box 
may  be  sunk  in  the 
bed  of  the  stream, 
leaving  its  rim  flush 
with  the  surface  over 
which  the  water  rolls. 
After  a  sufficient  in- 
terval remove  the  box 
and  dry  and  weigh 
the  material  collected. 
At  each  bend  in  a 
stream  soil  is  being 
taken  from  the  con- 
cave side  and  carried 
onward  toward  the 
sea,  while  on  the  op- 
posite side  new  soil  is 
being  formed  from 
that  dragged  along 
the  bottom.  In  this 
manlier  streams 
change  their  courses 

QTirl  -nTQTnrloT.  -f™™  oiVl«FlG-13-~  Pillar  Rock,  Wis.,  showhu?  rocky  cliff 
ana^vanaer  irom  Side  in  the  last  stages  of  decay.  (After  Chamber- 
tO  side  across  the  val-  lm>) 

ley,  each  time  making  a  new  soil  on  the  side  from  which 
they  are  retreating  and  carrying  away  an  older  soil  from 
the  encroaching  side.  It  is  in  this  way  that  broad  and 
flat  river  valleys  are  formed,  with  their  terraces,  such  as 
are  shown  in  Fig.  14.  It  is  in  this  way,  too,  that  the  "ox- 
bows" of  the  Mississippi  below  Vicksburg  were  formed, 
some  of  which  are  represented  in  Fig.  15. 

These  abandoned  river  channels  are  at  first  long  and 
narrow  lakes  but  ultimately,  with  the  repeated  overflows 
of  the  stream,  they  become  lilled.  Sometimes  they  remain 
for  long  intervals  depressions  in  which  swamp  or  humus 
soils  develop. 


56 


Physics  of  the  Soil. 


I 

tc 


Formation  of  Soil. 


FIG.  15. —  Showing  the  shifting  of  river  channels,  the  formation  of  "ox-bows" 
and  alluvial  soils. 

73.  Glacial  Soils. — In  those  portions  of  the  world  where 
the  temperature  is  so  low  that  most  of  the  moisture  falls 
as  snow  and  where  these  snows  do  not  all  melt  during  the 
warm  season  there  come  to  be  such  vast  accumulations  that 
the  great  weight  compresses  the  snow  into  ice.  So  ex- 
tensive and  massive  are  these  snow  and  ice  fields  in  Green- 


58 


Physics  of  the  Soil. 


Formation  of  Soil. 


60 


Physics  of  the  Soil. 


land  and  in  parts  of  Alaska  today  that  they  move  over  the 
face  of  the  country  much  as  a  broad  river  would  move, 
except  at  a  much  slower  rate.  The  same  type  of  phenom- 
ena occur,  too,  in  the  elevated  mountain  districts  of  Europe 
and  in  the  Sierras  of  this  country,  the  ice  streams  con- 
verging and  flowing  into  the  lower  valleys  in  the  form  of 
glaciers.  As  these  ice  streams  move  over  the  uneven  sur- 
face of  their  valleys  and  crowd  against  their  sides,  the 
rocks,  gravel  and  sand  taken  up  by  the  moving  ice  act  with 
great  effectiveness  to  abraid  into  soil  the  rigid  rock  surfaces 
over  which  they  move. 


FIG.  18. — Showing  rock  surface  over  which  glaciers  have  passed,  scratching  and 

polishing  it. 

In  a  recent  geological  epoch  the  whole  of  the  Xorth 
American  continent  north  of  the  Ohio  and  Missouri  rivers 
and  much  of  northern  Europe  and  Siberia  were  under  enor- 
mous moving  ice  sheets  which  resulted  in  the  formation 
of  the  extensive  glacial  soils  of  these  countries ;  consisting 
largely  of  a  rock  flour  ground  to  varying  degrees  of  fine- 
ness, and  naturally  very  fertile  where  the  materials  have 
not  been  sorted  by  the  waters  from  the  melting  ice  in  such 
a  way  as  to  form  siliceous  sandy  plains.  Figs.  16,  17,  18 
and  i9  are  views  illustrating  different  phases  of  soil  forma- 
tion by  glacial  action. 


Formation  of  Soil. 


61 


FIG.  19. —  Relief  Map  of  Wisconsin,  showing  the  difference  in  topography  be- 
tween glaciated  and  non-glaciated  surfaces. 


74.  Formation  of  Humus  Soils. — There  is  a  class  of  soils 
having  their  origin  in  various  types  of  swamps  or  marshes 
which  contain  an  unusual  amount  of  organic  matter  in  va- 
rious stages  of  decomposition  and  which  have  by  some 
writers  been  given  the  name  of  humus  or  swamp  soils,  the 
former  name  referring  to  the  large  amount  of  humus  these 
soils  contain  and  the  latter  to  the  physical  conditions  under 
which  they  have  been  formed. 

In  many  places  in  the  higher  latitudes  and  at  consider- 
able elevations  nearer  the  equator  where  the  surface  is  too 
flat  for  ready  drainage,  and  where  the  winter  snows  re- 
main so  long  upon  the  ground  that  the  summer  is  too  short 


62  Physics  of  the  Soil. 

to  permit  the  soil  to  become  dry  enough  to  allow  the  air 
to  penetrate  deeply  and  freely,  the  organic  matter  accu- 
mulates and  soils  are  formed  containing  a  large  proportion 
of  humus ;  even  beds  of  peat  may  develop. 

Under  other  conditions,  where  rivers  ap- 
proach their  outlet  across  a  very  flat  country 
g  and  are  no  longer  able  to  scour  their  chan- 
.2  nels  and  keep  them  clean,  the  moving  sedi- 
|  ment  finally  raises  the  banks  and  the  bed  un- 
*§  til  the  water  is  flowing  above  the  surround- 
=§  ing  country.  Under  these  conditions  with  a 
a  continual  seepage  and  frequent  overflows 
a  swamps  are  developed  in  which  marsh  vege- 
^  tation  grows  luxuriantly  and,  falling  under 
%  conditions  where  free  oxidation  cannot  oc- 
|  cur,  the  remains  only  partially  decay,  giving 

1  rise  to  beds  of  peat  and  rich  humus  soils. 

In  other  cases,  where  a  river  often  shifts 
|  its  course  and  especially  where  the  cut-offs 
"S  or  ox-bows  illustrated  in  Fig.  15  are  formed, 
|  these  places,  with  the  poor  drainage  which 
|  they  must  have  and  with  the  occasional  over- 
o  flows  to  keep  the  cut-offs  filled  with  water, 
"S  are  maintained  wet  long  and  continuously 
j§  enough  to  allow  humus  soils  to  form. 
|  With  the  final  withdrawal  of  the  great  ice 
*  sheet  from  the  glaciated  parts  of  America 
•S  and  Europe  there  were  left  large  numbers  of 
J5  shallow  lakes  whose  flat  margins  were  wet 
°\  enough  to  support  marsh  vegetation  and 
S  very  often  this  vegetation  came  to  form  a 

2  floating  fringe   steadily   encroaching   upon 
the  lake  in  the  manner  represented  in  Fig. 
20.     As  the  vegetation  continued  to  grow 

and  die  the  fringe  became  heavier  and  sank  more  deeply  in 
the  water  until  finally  the  whole  lake  was  overgrown  and 
until  the  organic  matter,  together  with  the  sediments 
brought  down  by  the  rains  and  the  w'inds  and  washed  in 


Formation  of  Soil. 


63 


from  the  surrounding  higher  land,  became  so  heavy  and  so 
thick  as  to  rest  upon  the  bottom  of  the  lake,  converting  it 
into  a  marsh  of  peat  or  humus  soil. 

On  the  margins  of  larger  lakes  and 
especially  along  the  seashore,  sand  bars 
or  reefs  are  thrown  up  behind  which 
bodies   of  water   are   shut   off   and  in  5 
these  organic  matter  may  accumulate  ti 
in  the  same  manner  as  that  just  de-  ^ 
scribed,  giving  rise  to  the  same  type  of  -f 
soils. 

In  still  other  cases,  on  the  margins  » 
of  the  sea  bottom,  there  flourishes  a  pe-  1 
culiar  type  of  vegetation  known  as  eel  ° 
grass,  which  lives  always  beneath  the  £ 
water  at  low  tide  in  a  position  repre-  g 
sented  in  Fig.  21.  These  grasses  offer  ?. 
a  natural  obstruction  to  the  incoming  g 
and  outgoing  tidal  waters,  causing  £ 
them  to  throw  down  their  sediments  B 
and  thus  build  up  the  sea  floor  with  ™ 
silt  containing  large  amounts  of  or-  & 
ganic  matter  under  conditions  unfav-  g 
orable  to  rapid  decay.  As  the  sea  floor  ? 
rises  in  this  way  above  low  tide  level  g* 
the  eel  grass  dies  and  another  type  of  g- 
swamp  vegetation  takes  its  place,  as  ™ 
between  a  and  b  in  the  figure,  and  here  j* 
again  the  formation  of  humus  soil  is 
continued  under  somewhat  different 
conditions. 

75.  Wind-Formed  Soils. — The  wind 
moving  continuously  over  the  face  of 
the  land  is  now  and  long  has  been  a  potent  factor  in  soil 
removal  and  soil  building.  Indeed,  it  is  probable  that 
nowhere  can  soils  be  found  which  do  not  contain  many 
wind-borne  particles.  Every  raindrop  which  falls  and 
every  snowflake,  however  white,  brings  to  the  field  upon 


64  Physics  of  the  Soil. 

which  it  falls  one  or  more  particles  of  soil  which  has  been 
drifting  in  the  higher  air  from  unknown  distances. 

The  drifting  of  dust  from  roads  during  dry  times  and 
from  fields  iii  the  spring  are  strong  reminders  of  the  po- 
tency of  wind  action  at  times,  but  it  is  the  less  evident  but 
continuous  action  that  counts  most  in  the  long  run  and, 
were  it  not  for  the  steady  wearing  away  and  rearrangement 
of  the  soil  surface,  wind-formed  soils  would  be  much  more 
evident  and  general  than  they  are. 

On  the  leeward  margins  of  arid  regions  and  on  sandy 
coasts  the  building  and  eroding  power  of  the  wind  becomes 
most  evident,  and  the  most  extensive  deposits  which  have 
been  assigned  to  this  cause  are  the  loess  beds  of  China 
which  have  great  horizontal  extent  and  in  some  places 
depths  reaching  even  1,200  and  2,000  feet.  These  depos- 
its have  been  described  by  llichthofen  as  having  been 
formed  from  dust  accumulations  drifted  by  the  prevailing 
winds  from  the  high  desert  plateaus  of  Central  Asia. 

In  Europe,  and  in  this  country  in  the  Mississippi  val- 
ley, there  are  deposits  of  a  similar  character.  They  are 
distributed  along  the  border  of  a  former  ice  sheet  of  the 
glacial  period  and  from  thence  they  spread  down  the  main 
streams,  along  the  Mississippi  from  Minnesota  to  near  the 
Gulf,  along  the  Missouri  from  Dakota  to  its  mouth,  and 
along  both  the  Illinois  and  the  Wabash.  These  deposits 
are  thickest,  most  typical  and  coarsest  along  the  bluffs 
nearest 'to  the  streams  and  they  thin  out  and  become  finer 
as  the  distance  back  increases.  It  is  thought  that  the  fine 
silts  borne  along  by  the  waters  of  the  glacial  streams  in 
times  of  high  water  were  spread  out  over  broad  flats  and 
as  the  ^.waters  withdrew  they  were  left  to  dry  in  the  sun 
and  then -picked  up  by  the  winds  and  drifted  away.  The 
loess  soils  are  almost  always  extremely  fertile  and  very  en- 
during. 

76.  The  Work  of  Animals  as  Soil  Producers Thci'e  are 

ninny  animals  which  have  contributed  largely  to  the  forma- 
tion of  soil  through  a  grinding  of  pebbles  and  the  coarser 
sand  and  soil  grains  into  finer  materials. 


Formation  of  Soil. 


65 


Darwin,  through  a  long  and  careful  study,  reached  the 
conclusion  that  in  many  parts  of  England  earthworms  pass 
more  than  10  tons  of  dry  earth  per  acre  through  their 
bodies  annually  and  that  the  grains  of  sand  and  bits  of  flint 
in  these  earths  are  partly  worn  to  fine  silt  by  the  muscu- 
lar action  of  the  gizzards  of  these  animals.  Their  method 
of  action  in  moving  through  the  soil  is  this  :  They  eat  a 
narrow  hole,  s\vallowing  the  earth,  when  the  point  of  the 
head  is  held  fast  in  the  excavation  while  an  enlarged  por- 
tion of  the  oesophagus  or  swallow  is  drawn  forward,  forc- 
ing the  cheeks  outward  in  all  directions,  thus  crowding  the 
soil  aside  and  making  the  opening  wider,  when  more  dirt 
is  eaten  and  the  operation  repeated,  allowing  the  animal 
to  advance  through  the  soil. 

Domestic  fowls  and  all  seed-eating  birds,  in  picking  up 
pebbles  for  service  in  grinding  their  food,  do  the  same  sort 
of  work  as  the  earth- 
worms in  producing 
fine  soil,  as  every 
housewife  can  testify 
from  the  worn  condi- 
tion of  bits  of  glass 
and  pottery  taken  from 
the  gizzard  of  the 
chicken. 

77.  Soil  Convection  — 
There  is  another  very 
important  line  of  work 
done  by  earthworms, 
ants  and  all  burrowing 
animals,  in  bringing 
the  sub-soil  to  the  sur- 
face and  carrying  the 
surface  soil  into  the 
ground,  thus  maintain- 
ing a  sort  of  soil-con- 

,«  i  •   i        •  f  FIG.  22.—  A  tower-liko  casting  ."ejected  by  a  spo- 

VeCtlOn     WniCn,     in     CI-        cies  of  earthworm,  from  the  Botanic  Garden, 


,^4-n     4-^ 
amounts     to 


Calcutta,  India.    Natural  size  from   photo. 
(After  Darwin.) 


66 


Physics  of  the  Soil. 


.  23  — Showimg  the  work  of  the  common  earth  worm  during  a  single  night  after 

a  heavy  rain. 


Formation  of  Soil. 


67 


same  thing  as  plowing  except  that  its  influence  extends 
much  deeper. 

Both  earthworms  and  ants  often  burrow  in  the  ground 
to  a  depth  of  four  feet,  and  in  some  cases  more  than  nine, 
bringing  the  material  to  the  surface  and  forming  passage- 
ways down  which  the  rains  may  wash  the  finer  surface 
soil.  Fig.  22  shows  a  single  pile  of  earth  cast  up  by  an 
earthworm  in  the  Botanic  Gardens  of  Calcutta,  and  Fig.  23 
shows  the  work  of  our  common  earthworm  during  a  single 
night  in  bringing  up  soil  after  a  rain. 


FIG.  21.— Section  of  vegetable  mould  in  a  field  drained  and  reclaimed  15  years 
before;  showing  turf,  vegetable  moulds  without  stones,  mould  with  frag- 
ments of  burnt  marl,  coal  cinders  and  quartz  pebbles  buried  under  the 
influence  of  earthworms.  Ono-third' natural  size.  (After  Darwin.) 

This  frequent  bringing  of  earth  to  the  surface  tends 
to  bury  objects  and  gradually  to  lower  them  into  the  ground, 
and  Fig.  24  represents  the  results  of  one  of  Darwin's 
studies,  showing  the  amount  of  soil  which  has  accumu- 


08  Physics  of  ike  Soil. 

lated  above  bits  of  burnt  marl,  cinders  and  pebbles  dur- 
ing 15  years,  largely  through  this  action  of  earthworms 
and  ants  in  bringing  to  the  surface  portions  of  the  sub- 
soil. It  will  be  seen  that  the  amount  accumulated  is  more 
than  three  inches,  or  at  the  rate  of  an  inch  in  5  years. 


CHAPTER  II. 

CHEMICAL  AND  MINERAL  NATURE  OF  SOILS. 

73.  Unsatisfactory  State  of  Present  Knowledge. — It  is 
now  pretty  generally  conceded  that  the  capacity  of  a 
soil  to  feed  crops  of  a  given  kind  cannot  be  foretold  with 
much  certainty  from  the  results  of  chemical  analyses  as  it 
has  been  the  custom  to  make  and  present  them.  It  has 
been  found,  for  example,  in  the  arid  west,  that  soils  nota- 
bly deficient  in  humic  nitrogen  and  which  for  this  reason 
should  be  comparatively  unproductive,  have,  nevertheless, 
been  found  capable  of  giving  large  yields  when  irrigated. 
Then  again,  in  moist  climates  there  are  types  of  soil  ex- 
ceptionally rich  in  both  humic  and  nitric  nitrogen  which 
are  comparatively  unproductive  until  they  are  given 
dressings  of  coarse  farmyard  manure.  The  analyst  would 
place  them  among  the  richest  of  soils  and  yet  they  are 
among  the  poorest  until  given  farmyard  manure;  and, 
what  appears  stranger  still,  straw  and  coarse  litter  may 
be  much  more  beneficial  to  them  than  liquids  from  the  sta- 
ble cistern. 

79.  Essential  Constituents  of  a  Fertile  Soil. — While  it  is 
true  that  our  chemical  knowledge  of  soils  is  very  unsatis- 
factory, it  has  nevertheless  been  thoroughly  established  that 
a  fertile  soil  must  contain  certain  substances  in  order  to 
permit  any  crop  to  come  to  maturity  upon  it  and  these  are 
potassium,  calcium,  magnesium,  phosphorus,  sulphur,  iron, 
nitrogen  and  probably  chlorine.  Let  any  one  of  these  ele- 
ments be  absent  from  a  soil,  or  its  moisture,  and  crops  fail 
to  develop  upon  it.  It  has  not,  however,  been  established  yet 
in  what  form  of  combination  these  elements  must  or  may 
exist  nor  in  what  proportions  to  give  the  best  results.  It 
is  known  that  they  do  not  exist  in  the  soil  in  the  elementary 
form  and  that  they  are  combined  in  a  great  variety  of  ways. 
5 


70  Physics  of  the  Soil. 

Furthermore,    from  these  combinations,    under  favorable 
conditions,  plants  are  able  to  supply  their  needs. 

80.  Functions  of  the  Essential  Plant  Foods. — From  the 
standpoint  of  plant  physiology  it  is  again  unfortunate  that 
little  has  yet  been  positively  demonstrated  regarding  the 
part  played  by  each  of  the  essential  elements  of  plant  food 
taken  through  the  soil  and  soil  moisture.  It  is  known  that 
nitrogen  is  an  essential  constituent  of  the  protein  com- 
pounds of  living  tissues,  and  that  to  most  of  the  cultivated 
crops  it  becomes  available  in  the  form  of  nitric  acid  or  of 
a  nitrate  of  lime,  magnesia,  potash  or  some  other  base.  Po- 
tassium does  not  appear  as  an  essential  ingredient  of  plant 
tissues  or  of  its  storage  products  like  starch  or  gluten,  but 
Nobbe,  Schroeder  and  Erdmann  have  shown  that  when 
Japanese  buckwheat,  placed  in  nutritive  solutions  en- 
tirely free  from  potash  salts,  after  a  few  weeks'  growth 
came  to  a  standstill  and  that  all  organs  of  the  plant  came 
to  be  nearly  or  quite  free  from  starch ;  but  when  a  potas- 
sium salt  was  added  to  the  solution  starch  began  to  develop 
and  growth  became  normal. 

In  regard  to  phosphorus  the  clearest  indications  go  to 
suggest  that  it  is  usually  taken  into  the  plant  in  the  form 
of  phosphates  and,  because  its  compounds  are  often  asso- 
ciated with  the  soluble  albuminoids,  that  it  assists  in  some 
way  in  the  transfer  of  these  from  place  to  place  in  the  plant. 

Some  compound  of  iron  must  exist  in  soil  solutions  and 
must  enter  the  plant  before  the  normal  development  of  the 
green  coloring  matter,  chlorophyll,  can  take  place;  so  ex- 
tremely small  quantities,  however,  are  needed  that  no  soil 
is  ever  lacking  in  sufficient  available  forms. 

Sulphur  is  apparently  largely  if  not  wholly  taken  into 
the  plant  in  the  form  of  sulphates,  and  these  are  thought  to 
be  decomposed  by  the  oxalic  acid,  setting  the  sulphuric  acid 
free,  which  is  then  broken  down  and  the  sulphur  appro- 
priated to  enter  as  an  essential  constituent  of  the  albumin- 
oid compounds. 

But  little  is  known  of  the  part  played  in  plant  life  by 


Chemical  Nature  of  Soils.  71 

the  salts  of  magnesium  except  that  they  must  be  present  in 
the  seed. 

The  action  of  lime  is  held  to  be  medicinal,  its  function 
being  to  neutralize  the  poisonous  oxalic  acid  liberated  a3 
an  intermediate  product  in  the  oxidation  of  carbohydrates. 

Largo  amounts  of  silica  and  alumina  and  smaller 
amounts  of  many  other  substances  are  found  in  the  ash  of 
plants  but  their  presence  there  is  regarded  as  accidental, 
growing  out  of  the  simple  fact  that  they  chanced  to  be  dis- 
solved in  the  soil-water  and  passed  into  the  tissues  with  it 
during  growth. 

81.  Chemical  Composition  of  Soils. — From  what  has  been 
said  regarding  the  origin  of  soils  and  the  manner  in  which 
their  particles  have  been  moved  from  place  to  place,  it  is 
evident  that  there  must  necessarily  be  a  strong  similarity 
among  them,  of  both  chemical  and  mineral  composition, 
wherever  found.     It  has  been  customary  in  analyzing  soils 
to  digest  a  certain  weight  of  dry  soil  for  a  stated  time  in  a 
certain  strength  of  hot  hydrochloric  acid  and  to  examine 
the  solution  for  the  compounds  it  might  contain,  calling  the 
part  not  dissolved  the  insoluble  residue.     The  tables  on 
pages  74-75  show  the  results  of  some  of  these  analyses, 
taken  from  the  papers  of  Hilgard  in  the  Tenth  Census  of 
the  United  States. 

82.  Chemical  Difference  Between  Clayey  and  Sandy  Soils. 

• — Studying  the  table  of  clayey  and  sandy  soils  it  will  be 
noted  that  out  of  every  100  pounds  of  the  clayey  soil  there 
were,  as  an  average,  31.791  pounds  which  dissolved  in  hot 
hydrochloric  acid,  while  only  G.79  pounds  were  soluble  in 
like  weight  of  the.  sandy  soil.  In  other  words,  a  quarter 
of  the  weight  of  the  clayey  soils  more  than  of  the  sandy  soils 
is  soluble  in  a  unit  of  time  in  hot  hydrochloric  acid.  There 
is  about  2.5  times  as  much  potash  and  organic  matter, 
nearly  twice  as  much  phosphoric  acid,  7  times  as  much 
lime,  9  times  as  much  magnesia  and  1.4  times  as  much 
sulphuric  acid  in  the  clayey  as  in  the  sandy  soil,  which 
may  be  dissolved  out  in  equal  times  by  the  solvent  used. 
These  ratios,  however,  are  sometimes  a  long  ways  from 


72  Physics  of  tlie  Soil. 

true  when  single  cases  are  compared,  and  this  is  shown  in 
a  striking  manner  in  the  single  case  of  clay  soil  given  below 
the  line  of  averages  in  the  table  of  sandy  and  clayey  soils. 
This  is  described  by  Hilgard  as  a  fair  upland  soil  yielding 
700  to  800  pounds  of  cotton  per  acre,  gray  in  color,  not 
heavy,  6  to  8  inches  deep,  and  underlaid  by  a  subsoil  quite 
heavy  in  tillage  and  dark  orange  in  color ;  and  yet  its  in- 
soluble residue  is  about  91  per  cent,  and  there  are  two  of 
the  sandy  soils  where  the  per  cents,  are  90  and  92  respec- 
tively, showing  that  the  two  are  more  nearly  alike  chemi- 
cally than  they  are  physically. 

83.  Observed  Chemical  Differences,  Partly  Due  to  Differ- 
ences in  Amount  of  Soil  Surface. — It  is  a  common  experience 
that  the  more  finely  a  substance  is  subdivided  the  more 
rapidly  will  it  dissolve.       Fine  salt  and  powdered  sugar, 
for  example,  dissolve  much  more  rapidly  in  water  than  the 
coarser  grained  varieties  do.     In  the  clay  soils  the  particles 
have  a  much  smaller  diameter  than  they  do  in  the  sandy 
soils  and  hence  the  number  of  grains  in  a  given  weight  of 
soil  will  be  much  larger,  but  the  number  of  grains  cannot 
be   increased   without   also   increasing   the  surface   upon 
which   the  solvent   may   act,    and   hence   with   the   same 
strength  and  amount  of  acid,  for  equal  weights  of  the  coarse 
and  fine  grained  soil,  having  exactly  the  same  chemical 
composition,  there    should  be  dissolved    in  equal    times  a 
larger  per  cent,  of  the  soil  having  the  largest  amount  of  sur- 
face.    The  sandy  soils  therefore  are  not  likely  to  be  as  dif- 
ferent from  the  clayey  ones  as  the  table  of  analyses  indi- 
cate. 

84.  The   Chemical   Differences   Between  Soils   and  Their 
Subsoils. — In  humid  climates  there  is  usually  a  marked  dif- 
ference in  the  producing  capacity  of  the  soils  and  their  sub- 
soils as  was  pointed  out  in  (65),  and  a  study  of  the  table 
of  subsoils,  pp.  74,  75,  will  show  that  there  is  a  chemical 
difference  also.     It  will  be  seen  that  the  surface  soils  con- 
tain more  lime,  phosphoric  acid  and  organic  matter,  less 
soluble   silica,    alumina   and   iron   and    about   the   same 
amounts  of  potash,  magnesia  and  sulphuric  acid. 


Chemical  Nature  of  Soils.  73 

85.  Comparison  Between  Clay  Soils  and  Swamp  Soils. — If 
a  comparison  is  made  between  the  clayey  soils,  which  are 
generally  productive  naturally,  and  the  humus  soils  it  will 
be  seen  that  the  latter  contain  about  twice  as  much  potash, 
magnesia,  sulphuric  acid  and  organic  matter,  six  times  as 
much  lime  and  a  little  more  phosphoric  acid,  and  yet  for 
some  reason  the  humus  soils,  when  well  drained,  may  not 
naturally  be  as  productive  as  the  clay  soils  are  and  here  is 
where  the  present  methods  of  soil  analysis  fail  to  tell  the 
whole  truth. 

86.  Comparison  Between  Clayey  Soils  and  Loess  Soils. — 
The   loess  soils    do  not  show    a    much   larger    percentage 
amount  of  the  essential  ingredients  of  plant  food  than  do 
the  clayey  ones.  Indeed  there  is  less  of  organic  matter  and 
only  a  little  more  of  potash,  phosphoric  and  sulphuric  acids. 
The  chief  and  great  difference  lies  in  the  large  amount  of 
lime  and  magnesia  which  they  contain,  the  first  being  more 
than  9,  and  the  latter  more  than  8  times  as  large.     If  it  is 
true  that  these  soils  are  largely  wind-formed  it  is  to  be  ex- 
pected that  these  A  wo  substances  would  appear  at  the  sur- 
face to  be  taken  up  by  the  winds  more  than  any  other  of  the 
essential  ingredients,  first,  because  they  are  comparatively 
soluble  and  bence  likely  to  be  brought  up  by  the  capillary 
waters  and  left  after  evaporation  where  the  wind  has  free 
access  to  them ;  and  second,  because  they  are  not  so  soluble 
as  to  be  completely  dissolved  by  the  heavy  rains  and  car- 
ried back  into  the  ground  again. 

87.  Difference  Between  Arid  and  Humid  Soils. — The  soils 
which  have  accumulated  in  the  arid  climates  of  the  world 
are  quite  markedly  different  from  those  of  the  more  humid 
portions,  both  in  physical  and  chemical  properties.     The 
per  cents,  given  in  the  table  of  arid  and  humid  soils  are 
those  of  Hilgard  and  are  averages  of  466  analyses  from  hu- 
mid climates  and  313  from  arid. 

It  will  bp  seen  that  the  arid  soils  contain  more  than  3 
times  as  much  potash,  nearly  13  times  as  much  lime  and  6 


Physics  of  the  Soil. 


Chemical  composition  of  soils. 

Essential  ingredients  in  per  cent   of  dry  soil. 


POTASH. 

LlUE. 

MAGNESIA. 

PHOSPHOR- 
IC ACID. 

SULPHURIC 
ACID. 

WATEB 
AND  ORGANIC 

MATTER. 

Sand. 

Clay. 

Sand 

Clay. 

Sand. 

Clay. 

Sand. 

Clay. 

Sand. 

Clay. 

Sand. 

Clay. 

.100 

.416 

.120 

.080 

.040 

.691 

.051 

.103 

.028 

.061 

2.055 

1.006 

.156 

.176 

.081 

•090 

.069 

.112 

.101 

.071 

.Or«7 

.055 

2.642 

8.891 

.015 

.186 

.064 

.071 

.005 

.065 

.066 

.204 

.091 

.285 

2.  422 

8.9S3 

.117 

.134 

.058 

.219 

.042 

.289 

.092 

.069 

.058 

.035 

1.807 

8.309 

.110 

.242 

.090 

.387 

.025 

.508 

.191 

.071 

.105 

.055 

3.477 

6.843 

.067 

.092 

.119 

.036 

.090 

.070 

.111 

.082 

.054 

.054 

2.881 

6.167 

.275 

.431 

.055 

.540 

.048 

.836 

.105 

.187 

.001 

.009 

3.682 

6.922 

.095 

1.104 

.076 

1.349 

.083 

1.665 

.0.(9 

.304 

.045 

.024 

2.354 

7.369 

.209 

.150 

.141 

3.054 

.031 

.0:29 

.103 

.24i 

.046 

.089 

3.113 

4.962 

.034 

.255 

.045 

.340 

.013 

.296 

.014 

.079 

.035 

.079 

1.636 

4.962 

.121 

.319 

.085 

.617 

.048 

.456 

.037 

.141 

.055 

.075 

2.607 

6.528 

.137 

.173 

.203 

.038 

3.394 

SWAMP  AND  LOESS  SOILS. 


Hu- 
mus 

Loess 

Hu- 
mus. 

Loess 

Hu- 
mus 

Looss 

Hu- 
mus. 

Loess 

Hu- 
mus. 

Loess. 

Hu- 
mus. 

Loess. 

.639 

.435 

3.786 

5.820 

.886 

3.C02 

.150 

.203 

.148 

.090 

13.943 

1.205 

SOILS  COMPARED  WITH  THEIR  SUG-SOILS. 

SOILS. 


Sand. 

Clay. 

Sand 

Clay. 

Sand 

Clay. 

Sand 

Clay 

Sand. 

Clay. 

Sand. 

Clay. 
6.014 

.157 

.214 

.115 

1.761 

.076 

.182 

.128 

.207 

052 

.030 

2.853 

SUB-SOILS. 


.143 

.314 

.096 

1.481 

.073 

.240 
—.058 

.124 

.150 

.060 

.071 

1.9J3 

4.780 

•}-.  014 

-.130 

+  019 

+  .280 

+.003 

+.004 

+  .018 

-.008 

+.019 

+.910 

+1.234 

ARID  AND  HUMID  SOILS  COMPARED. 


Hu- 
mid. 

Arid. 

Hu- 
mid. 

Arid. 

Hu- 
mid. 

Arid. 

Hu- 
mid. 

Arid. 

Hu- 
mid. 

Arid. 

Hu- 
mid, 

Arid. 

.216 

.729 

.103 

1.362 

.225 

1.411 

.113 

.117 

.052 

.041 

3.644 

4.945 

Chemical  Nature  of  Soils. 


Chemical  composition  of  noils. 

Inert  ingredients  in  per  cent,  of  dry  soil. 


BROWN 

INSOLUBLE 
RESIDUE. 

SOLUBLE 
SILICA. 

SODA. 

OXIDE  OF 
MAN- 

PEROXIDE 
or  IEON. 

ALUMINA. 

GANESE. 

Sand. 

Clay. 

Sand 

Clay. 

Sand 

Clay. 

Sand 

Clay. 

Sand 

Clay. 

Sand. 

Clay 

93.630 

72.746 

1.682 

8.9:!6 

.000 

.112 

.102 

.106 

.761 

12  406 

1.532 

2.473 

94  770 

73  690 

.488 

3.370 

.069 

.004 

.156 

.146 

.706 

5.939 

.7*3 

7  305 

93.882 

60.3-0 

1.721 

2.000 

.018 

.119 

.220 

.196 

.941 

9.709 

1.33;) 

IS  0*16 

05.690 

73.422 

.879 

2.70) 

.OS4 

trace 

.4)49 

.164 

.224 

4.054 

.473 

10.598 

92.0UO 

63.444 

1.220 

11.325 

.035 

.079 

.126 

.052 

.963 

3.894 

1.959 

13.454 

90  230 

77.880 

1.940 

1  790 

.009 

.041 

.313 

.056 

1.927 

5.6461 

2.141 

7.  538 

90.  CM 

54  565 

1.8X5 

13  219 

.130 

.277 

.172 

.079 

1.837 

7.089 

1.436 

1C.  071 

9^  460 

51.0(53 

1.650 

20  701 

.036 

.325 

.040 

.119 

.843 

5.818 

2.649 

10.539 

94.  4  'is 

79  5.HO 

.529 

3.628 

.069 

.065 

.101 

.195 

.661 

3.4-20 

1.185 

4.9N-* 

94.822 

75.350 

1.03J 

7.310 

.022 

.258 

.020 

.038 

.930 

5.784 

1.576 

5.567 

93.210 

68.203 

1.293 

7.498 

.051 

.128 

.130 

.115 

.979 

6.381 

1.503 

9.660 

91.49S 

1.722 

.054 

.066 

1.372 

1.522 

SWAMP  AND  LOESS  SOILS. 


Hu- 
mus. 

Loess. 

Hu- 
mus. 

Loess. 

Hu- 
mus. 

Loess 

Hu- 
mus. 

Loess 

Hu- 
mus. 

Loess 

Hu- 
mus. 

Loess 

35.886 

68.853 

20825 

4.913 

.109 

.165 

.098 

.164 

7.040 

3.569 

14.476 

2.812 

SOILS  COMPARED  WITH  THEIR  SUB-SOILS. 

SOILS. 


Sand. 

Clay. 

Sand 

Clay. 

Sand 

Clay, 

Sand 

Clay. 

Sand 

Clay. 

Sand. 

Clay. 

93.222 

73.978 

1.019 

5.034 

.072 

.085 

.124 

.133 

1.162 

5.205 

1.145 

6.993 

SUB-SOILS. 


90.714 

66.290 

2.212 

7.446 

.061 

.085 

.080 

.125 

1.739 

6.947 

2.276 

12.036 

+2.508 

+7.688 

-1.193 

-2.412 

+  .003 

.000 

+.014 

+.003 

—.577 

-1.742 

—1.131 

-5.083 

ARID  AND  HUMID  SOILS  COMPARED. 


Hu- 
mid. 

Arid. 

Hu- 
mid. 

Arid. 

Hu- 
mid. 

Arid. 

Hu- 
mid. 

Arid. 

Hu- 
mid. 

Arid. 

Hu- 
mid. 

Arid. 

S4.031 

70.565 

4.212 

7.266 

.091 

.264 

.133 

.059 

3.131 

5.752 

4.296 

7.883 

76  Physics  of  the  Soil. 

times  as  much  magnesia  as  do  the  humid  soils  with  which 
they  have  been  compared.  They  also  contain  some  more  of 
each  of  the  other  essential  plant  foods  except  sulphur,  the 
sulphuric  acid  being  less. 

If,  however,  a  comparison  is  made  between  the  arid  soils 
and  the  mean  of  the  10  clay  soils  given  in  the  first  table, 
it  will  be  seen  that,  excepting  potash,  lime  and  magnesia, 
these  contain  more  of  the  essential  ingredients  of  plant 
food  than  do  the  arid  soils,  and  so,  too,  there  is  more  solu- 
ble silica. 

88.  Humus. — It  is  this  product  in  the  soil  which  gives  to 
it  usually  its  dark  color,  but  so  far  as  its  chemical  composi- 
tion is  concerned  its  nature  is  not  yet  well  understood.     It 
is  a  very  important  ingredient  of  fertile  soils  and  is  the 
product  of  decaying  organic  matter, 

In  torrid  climates  where  the  scil  is  warm  the  whole  year 
and  in  arid  regions  where  the  soil  is  more  open  on  account 
of  deficient  moisture  as  well  as  on  sandy  soils  wherever 
found,  the  rate  of  complete  decay  is  so  rapid  that  the 
amount  of  humus  is  generally  relatively  small ;  but  in  tem- 
perate climates,  where  the  soil  is  damp,  its  texture  close  and 
rains  frequent,  the  organic  matter  decays  more  slowly  and 
the  amount  of  humus  in  the  soil  is  relatively  greater. 

The  great  importance  of  humus  in  agricultural  soils  is 
found  in  the  fact  that  it  is  relatively  insoluble  under  good 
field  conditions  and  does  not  leach  away  and  in  this  form 
becomes  the  food  of  niter-forming  germs  which  convert  it 
by  degrees  into  nitric  acid,  as  one  of  their  waste  products, 
but  the  essential  form  of  nitrogen  for  the  food  of  most 
higher  plants.  A  soil  entirely  devoid  of  humus  must  neces- 
sarily be  manured  or  given  nitrogen  in  some  other  form 
in  order  to  make  it  fertile. 

89.  Difference  Between  the  Humus  of  Arid  and  Humid  Cli- 
mates.— Hilgard  and  Jaffa  have  made  the  important  dis- 
covery that  the  humus  of  arid  soils  is  relatively  richer  in 
nitrogen  than  is  that  of  humid  soils  and  hence  that  smaller 


Chemical  Nature  of  Soils. 


77 


amounts  of  it  will  meet  the  needs  of  niter-forming  germs 
and  thus  allow  large  crops  to  be  produced  where,  with  a 
poor  form  of  humus,  this  would  be  impossible. 

The  results  of  their  studies  in  this  line  are  stated  in  the 
table  below : 


No.  of 
samples. 

Humus  in 
soil. 

Nitrogen 
in  humus. 

Humic 
nitrogen  in 
soil. 

18 

Per  cent. 
.75 

Per  cent. 
15  87 

Per  cent. 
101 

g 

.99 

10  03 

.102 

8 

3.0t 

5  24 

.132 

In  speaking  of  these  results  they  say,  "It  thus  appears 
that,  on  the  average,  the  humus  of  the  arid  soils  contains 
three  times  as  much  nitrogen  as  that  of  the  humid,  that  in 
the  extreme  cases  the  nitrogen  percentages  in  the  arid  hu- 
mus actually  exceeds  that  of  the  albuminoid  group,  the 
flesh-forming  substances." 

"It  thus  becomes  intelligible  that  in  the  arid  region  a 
humus  percentage,  which,  under  humid  conditions,  would 
justly  be  considered  entirely  inadequate  for  the  success  of 
normal  crops,  may,  nevertheless,  suffice  even  for  the  more 
exacting  crops.  This  is  more  clearly  seen  on  inspection  of 
the  figures  in  the  third  column,  which  represent  the  product 
resulting  from  the  multiplication  of  the  humus  percentages 
of  the  soil  into  the  nitrogen  of  the  humus." 

90.  Chemical  Composition  of  Soils  Compared  With  the 
Rock  from  Which  They  Are  Derived. — When  a  soil  accumu- 
lates in  place  from  slow  decomposition  of  the  underlying 
rock  there  is  sometimes  a  close  resemblance  in  chemical 
composition  between  the  rock  and  the  derived  soil,  but  in 
other  cases  there  is  little  resemblance  between  them.  If 
the  rock  is  made  up  of  a  large  percentage  of  relatively  solu- 
ble materials,  as  is  the  case  with  most  limestones,  then  the 
solvent  power  of  water,  combined  with  the  effects  of  leach- 
ing, tend  to  cause  a  concentration  of  the  relatively  insoluble 


78 


Physics  of  the  Soil, 


ingredients,  thus  giving  rise  to  a  soil  very  different  in  chem- 
ical composition  from  the  parent  rock. 

If,  on  the  other  hand,  the  rock  is  made  up  of  minerals  of 
nearly  equal  solubilities,  or  if  in  any  way  the  soil  results 
from  a  mechanical  breaking  up  of  the  rock,  then  the  soil 
may  have  much  the  same  relative  amounts  of  ingredients  as 
the  parent  rock  shows.  In  the  table  which  follows  are 
given  the  composition  of  some  rocks  and  of  soils  derived 
directly  from  them: 

Composition  of  rocJcs  and  residual  soils. ] 


'TRENTON 
LIMESTONE 

BERMUDA 
LIMESTONE 

GNEISS, 

GRANITE. 

DlOBITB. 

Rock 

Soil. 

Rock 

Soil. 

Rock 

Soil. 

Rock 

Soil. 

Rook 

Soil. 

Prct. 

Prct. 

Prct. 

Pr  ct 

Prct. 

Prct. 

Prct. 

Prct. 

Prct. 

Prct. 

Silica  (SiO2)  .... 

.44 

43.07 

.052 

45.16 

60.69 

45.31 

69.33 

65.69 

46.75)  42.44 

Alumina  (A^Os) 

.042 

25.07 

0  .54 

15  473 

16.89 

26  55 

14.33  15.23 

17.fi! 

25.51 

Ferric  oxide  

15.16 

13.898 

9.16 

12.18 

3.60J  4.39 

16.79 

19.20 

Lirno  (CaO)  

ti'.ii' 

0.63 

54  '496 

3.948 

4.41 

tr. 

3.211  2.63 

9.46 

0.37 

Magnesia  (MgO) 

tr. 

0.03 

1.751 

0.539 

1.06 

0.40 

2.44    2.64 

5.12 

0  21 

Potash  (KzO)  ... 

notd. 

2.50 

0.06S 

0.133 

4.25 

1.10 

2.67 

2.00 

0.55 

0.49 

Soda  (Na2t>)  — 

notd. 

1.20 

0.252 

0.007 

2.42 

0.22 

2.70 

2.12 

2.56 

0  56 

Carbon  dioxide.. 

42.72 

tr. 

44.251 

2.533 

0.00 

0.00 

0.00 

Phos.  acid  (PaOs) 

0.47 

'6!io 

6!66 

0.25 

0.29 

Water  and  vola- 

tile products  .. 

1.03 

12.98 

.32* 

18.265 

.62 

13.75 

11.22 

4.70 

0.92 

10.92 

The  two  limestones,  it  will  be  seen,  have  given  rise  to  a 
soil  containing  almost  as  much  silica,  alumina  and  iron 
oxide  combined  as  is  contained  in  the  three  soils  from  the 
other  three  kinds  of  rock,  the  per  cents,  standing,  in  round 
numbers,  83,  75,  84,  85  and  87.  In  other  words  there  is 
a  strong  tendency  to  bring  all  soils  approximately  to  one 
composition.  Indeed  it  may  be  said  that  in  any  soil  the 
essential  ingredients  of  plant  food  make  up  but  from  3  to 
8  per  cent,  of  the  total  dry  weight.  It  will  be  observed 
that  in  the  case  of  the  soil  derived  from  the  Bermuda  lime- 
stone, not  less  than  98  pounds  of  every  100  pounds  of  rock 


i  Rocks,  Rock  Weathering  and  Soils.     Merrill. 


Chemical  Food  in  Soils. 


79 


arc  dissolved  and  carried  away  by  the  water  for  each  2 
pounds  of  soil  formed,  the  chief  materials  carried  away 
being  the  lime,  magnesia  and  carbon  dioxide. 

91.  Amount  of  Essential  Plant  Food  Removed  from  the 
Soil  by  Crops. — It  is  very  important,  in  the  management  of 
soils,  to  know  something  of  the  draught  upon  them  which 
crops  of  different  kinds  make,  and  in  the  table  which  fol- 
lows is  given  the  amount  of  materials  removed  from  the 
soil  in  1,000  pounds  of  fresh  or  air-dried  product. 

Table  showing  Ibs.  of  plant  food  in  1000  Ibs.  oj  air-dried 
product. 

(WOLFF.) 


MAIZE. 

OATS. 

WTNT'E 
WHEAT 

SPRING 
WHEAT 

WINT'B 
RYE. 

BARLEY 

BED 
CLOVEB 

It 
id 
E 

<B 

_g 
'3 

E 

O 

It 

1 

03 

_a 

'3 

5 

EC 

2 
& 

03 

a 
'3 

S*i 

O 

Be 

a 
c 
& 

03 

a 

S 

- 

Bt 

C3 
E 
S 

03 

a 

£ 
o 

a 

Ki 

03 

a 

'3 
t-> 

O 

& 

C3 
fa 

03 

a 

S 
3 

Total  ash  
Potash  (K8O)  ... 
Soda  (NaaO)    ... 
Magnesia  (MgO) 
Lime  (CaO)  
Fhos  acid  iPgOs) 
Sul.  acid  (SOs).. 
Sulphur  
Nitrogen  

45.3 
16.4 
.5 
2.6 
4.9 
3.8 
2.4 
3.9 
4.8 

12.4 
3.7 
0.1 
1.9 
0.3 
5.7 
0.1 
1.2 
16.0 

61.6 
16.3 
2.0 
2.3 
4.3 
28 
2.0 
1.7 
5.6 

26.7 
4.8 
1.0 
1.9 
1.0 
6.8 
0.5 
1.7 
17.6 

46.0 
6.3 
0.6 
1.1 

2.7 
2.2 
1.1 
1.6 

4  X 

16.8 
5.2 
0.3 
2.0 
0  5 
7.9 
0.1 
1.5 
20.8 

.«.! 
11.6 
1.0 
0.9 
2  6 
2.0 
1.2 

'.V6 

18.3 
5.6 
0.31 
2.2 
0.5 
9.0 
0.2 

20'5 

38.2 
8.6 
0.7 
1.2 
3.1 
2.5 
1.6 
0.9 
4.0 

17.!) 
5.8 
03 
2.0 
0  5 
8.5 
0.2 
1.7 
17.6 

45.9 
10.7 
1.6 
1.2 
3  * 
1.9 
1.8 
1.3 
6.4 

22.3 
4.7 
0.5 
2.0 
0.6 
7.8 
0.4 
1.4 
16.0 

57.6 
18.6 
1  1 
6.3 
20.1 
5.6 
1.6 
2.1 
19.7 

38.3 
13.5 
0.4 
4.9 
2.5 
14.5 
0.9 

30  '.5 

From  this  table  it  appears  that  each  ton  of  clover  hay 
withdraws  from  the  soil  39.4  Ibs.  of  nitrogen;  37.2  Ibs.  of 
potash ;  12.6  Ibs.  of  magnesia  ;  40.2  Ibs.  of  lime ;  11.2  Ibs.  of 
phosphoric  acid ;  and  14.2  Ibs  of  sulphuric  acid,  making 
an  aggregate  of  ash  ingredients  alone  of  154.8  Ibs. 

92.  Amount  of  Plant  Food  in  an  Acre-foot  of  Soil. — If  we 
take  4,000,000  pounds  as  the  dry  weight  of  an  acre-foot  of 
all  soils,  except  the  humus  and  that  at  2,000.000  (149), 
and  the  percentages  of  essential  plant  food  given  in  the 
tables  on  pages  74  and  75,  the  amount  of  plant  food  per 
acre-foot  may  then  be  computed,  giving  the  results  in  the 
table  below: 


80 


Physics  of  the  Soil. 


Table  giving  the  tons  of  essential  plant  food  per  acre-foot 
of  different  types  of  soil. 


Sandy  soil. 

Clay  soil. 

Loess  soil. 

Humus 
soil. 

Potash  (KgO)  

Tons. 
2  42 

Tons. 
6  38 

Tons. 
8  70 

Tons. 
6  39 

Lime  (CaO)  

1.70 

12  at 

116  40 

37  86 

Magnesia  (MgO)  

.96 

9.12 

73.84 

8  68 

Phosphoric  acid  (PvOs)  

1.74 

2.82 

4.00 

1  M3 

Sulphuric  acid  (SOj)  

1.10 

1.50 

1.80 

1  48 

From  this  table  it  appears  that  the  amount  of  plant  food 
per  acre-foot  of  field  soils,  not  including  nitrogen,  ranges 
from  about  2  to  8  tons  of  potash,  2  to  116  tons  of  lime, 
1  to  73  tons  of  magnesia,  2  to  4  tons  of  phosphoric  acid, 
and  1  to  2  tons  of  sulphuric  acid. 

93.  Number  of  Crops  Required  to  Kemove  the  Plant  Food 
of  an  Acre-foot  of  Soil. — The  ratio  of  dry  weight  of  the  ker- 
nels to  that  of  the  straw  and  chaff  in  a  crop  of  wheat  has 
been  found  to  be  as  1  to  1.1  in  a  dry  season,  but  to  be  as 
high  as  1  to  1.5  when  there  has  not  been  an  undesirable 
stimulation  to  the  growth  of  straw.  Taking  this  ratio  of 
1  to  1.5,  a  yield  of  40  bushels  of  wheat  per  acre  would 
mean  a  crop  of  2,400  Ibs.  of  grain  and  3,600  Ibs.  of  straw. 
From  these  two  figures,  the  data  in  the  table  of  (91)  and 
that  of  (92),  it  is  possible  to  compute  the  number  of  ci-ops 
of  wheat  yielding  40  bushels  per  acre  which  would  remove 
the  amount  of  plant  food  in  an  acre-foot  of  one  of  the  sev- 
eral types  of  soil  represented  in  the  table  of  (92).  Solv- 
ing the  problem  for  the  potash  in  the  clay  soil  the  case 
would  be 


6.38  X  2,000 


(2.4X5.2) +  (3.6X6.3) 


=  362.9 


Plant  Food  in  Soils.  81 

where  6.38  is  the  tons  of  potash  per  acre-foot, 
2,000  is  the  number  of  Ibs.  in  one  ton, 
2.4  is  the  number  of  1,000  Ibs.  of  grain  in  40  bush,  of  wheat, 

5.2  is  the  number  of  Ibs.  of  potash  per  1,000  Ibs.  of  grain, 
3.6  is  the  number  of  1,000  Ibs.  of  straw  with  40  bush,  of  wheat 

6.3  is  the  number  of  pounds  of  potash  per  1,000  Ibs.  of  straw, 
362.9  is  the  number  of  crops  of  wheat. 

When  the  problem  is  solved  for  each  of  the  essential 
plant  foods  used  by  the  wheat  crop,  the  results  will  stand 
for  the  clay  soil  as  given  below : 

Potash  enough  for  363  crops  of  wheat  of  40  bush,  per  acre. 
Magnesia  enough  for  2,082  crops  of  wheat  of  40  bush,  per  acre. 
Lime  enough  for  2,260  crops  of  wheat  of  40  bush,  per  acre. 
Phosphoric  acid  enough  for  210  crops  of  wheat  of  40  bush,  per 

acre. 
Sulphuric  acid  enough  for  108  crops  of  wheat  of  40  bush,  per 

acre. 
Nitrogen  enough  for  78.5  crops  of  wheat  of  40  bush,  per  acre. 

In  computing  the  nitrogen  in  the  soil  for  this  table  .132 
per  cent,  from  the  table  in  (89),  was  taken  and  the  same 
weight  of  soil,  4,000,000  pounds  per  acre-foot  as  used  for 
the  other  plant  foods. 

It  has  been  assumed  that  40  bushels  of  grain  and  3,600 
pounds  of  straw  per  acre  are  taken  from  the  ground  each 
crop  and  that  nothing  is  returned  to  the  soil,  and  yet  chem- 
ical analyses  would  indicate  that  there  is  enough  of  every- 
thing but  nitrogen  for  more  than  a  century  of  cropping, 
and  this  is  saying  nothing  regarding  the  plant  food  which 
is  known  to  exist  in  the  second,  third  and  fourth  feet  of  soil 
in  which  the  roots  of  plants  regularly  feed.  Plainly  we 
have  very  important  knowledge  yet  to  discover  regarding 
the  feeding  of  plants  from  the  soil. 

94.  Experiments  at  Rothamstead — The  classic  experi- 
ments which  have  been  made  by  Sir  J.  B.  Lawes  and  his  as- 
sociates regarding  the  conditions  which  determine  the  fer- 
tility of  the  soil,  have  thrown  much  needed  light  upon  this 


82  Physics  of  the  Soil. 

problem.  By  growing  the  same  crop  year  after  year  on  the 
same  ground  to  which,  no  nitrogen-bearing  manures  were 
applied,  they  learned  that  when  fertilizers  containing  the 
essential  ash  ingredients  of  the  plant  were  added  to  the 
soil  larger  yields  and  more  nitrogen  could  be  taken  from 
the  ground. 

They  found  that  when  wheat  grown  continuously  for  32 
years  on  the  same  soil  without  manure  of  any  sort  could 
obtain  but  20.7  Ibs.  of  nitrogen  per  acre,  the  same  crop  on 
adjacent  and  similar  land  given  fertilizers  without  nitrogen 
could  gather  22.1  Ibs.  or  6.76  per  cent.  more.  Barley, 
which,  with  no  fertilizers,  during  24  years  could  gather  but 
18.3  Ibs.  per  acre  per  annum,  did,  when  aided  with  other 
ash  ingredients,  remove  from  the  soil  22.4  Ibs.  of  nitrogen 
per  acre.  Beans,  which  gathered  from  untreated  land  31.3 
Ibs.  of  nitrogen  per  acre  during  24  years,  took  off  from  the 
land  under  the  other  treatment  45.5  Ibs.  per  acre.  So, 
too,  in  a  rotation  of  crops,  7  courses  in  28  years,  no  fertil- 
izers gave  36.8  Ibs.  of  nitrogen,  while  with  superphosphate 
of  lime  the  yield  was  45.2  Ibs.  per  acre.  Again  in  the 
mixed  herbage  of  grass  land  20  years  without  fertilizers 
gave  33  Ibs.  of  nitrogen  per  acre,  but  where  mixed  mineral 
fertilizers  containing  potash  were  given  the  yield  was  55.6 
Ibs.  of  nitrogen  per  acre. 

95.  Store  of  Nitrogen  in  the  Soil. — The  mean  amount  of 
nitrogen  in  eleven  arable  and  grass  soils  at  Rothamstead  is 
placed  by  Lawes  and  Gilbert  at  .149  per  cent,  and  for  eight 
other  Great  Britain  soils  at  .166  per  cent.     Voelcker  found 
in  four  Illinois  prairie  soils  .308  per  cent.,  and  C.  Schmidt 
gives  for  seven    rich  Russian  soils    .341  per  cent.       The 
mean  of  these  30  analyses  is  .219  per  cent,  and  yet  a  soil 
containing  but  .1  per  cent,  will  carry  4,000  Ibs.  or  enough 
for  nearly  60  40-bushel  crops. 

96.  Amount  of  Nitrogen  in  Four  Manitoba  Soils. — As  an 
example  of  soils  exceptionally  rich  in  nitrogen  the  table 


Nitrogen  in  Soils. 


below  gives  the  distribution  and  amount  per  acre  in  each 
of  the  upper  four  feet  of  four  Manitoba  soils: 


Niverville. 

firandon. 

Selkirk. 

Winnipeg. 

First  foot  

Lbs. 
7,308 

Lbs. 
5  236 

Lbs. 
17  304 

Lbs. 
1]  984 

5,408 

3.48S 

8,448 

10,464 

Third  foot  

2,484 

2,  592 

2,736 

5,fiM8 

Fourth  foot  

1,520 

870 

1,4»7 

4  045 

Total  

16,  720 

12,  186 

29,  975 

3^,181 

Tons  

8  36 

6  093 

14  987 

16  09 

Thus  it  is  seen  that  in  the  upper  four  feet  of  these  rich 
soils  there  was  found  from  6  to  16  tons  per  acre  of  nitrogen. 

97.  Forms  in  Which  Nitrogen  Occurs  in  the  Soil. — Nitro- 
gen occurs  in  the  soil  in  several  distinct  forms : 

1.  In  humus,  described  in  (88);  which  is  by  far  the  most 
important  form  and  the  substance  which  carries  the  largest 
proportion  of  that  which  the  soil  contains. 

2.  In  organic  matter  in  the  form  of  roots,  stubble  and 
farmyard  manure,  which  by  slow  degrees  is  converted  into 
humus  to  make  good  that  which  bus  been  used. 

3.  As  free  nitrogen  in  soil-air  which  is  seized  upon  by 
some  forms  of  microscopic  life  described  in  (101)  and  con- 
verted into  organic  form  for  their  use. 

4.  As  nitrates  of  lime,  magnesia,  potash  and  soda,  and 
this  is  the  form  from  which  most  of  the  higher  plants  get 
their  supply. 

5.  As  ammonia,  nitrous  acid  and  nitric  acid,  which  are 
transition  stages  to  one  of  the  nitrates  named  above  and 
which  are  formed  either  from  the  humus  or  organic  matter 
or  are  brought  down  with  the  rain. 

98.  Distribution  of  Nitrogen  in  the  Soil — In  humid  cli- 
mates the  largest  amount,  of  nitrogen  is  found  in  the  surface 
6  to  12  inches,  but  as  already  shown  in  (96)  large  quan- 
tities are  found  as  deep  as  four  feet  below  the  surface. 


fi4 


Physics  of  the  Soil. 


Warington  determined  the  distribution  of  nitrogen  in 
some  of  the  Rothamstead  soils  to  a  depth  of  9  feet  in  9-inch 
sections.  The  results  he  found  are  given  in  the  table  be- 
low: 

Nitrogen  in  soils  at  various  depths. 


Arable  soils. 

Old  pasture. 

Lbs.  per  acre 
3,015 

Lbs.  per  acre 
5,351 

1,629 

2,313 

1,461 

1,580 

1/228 

1,412 

1,090 

1,301 

1,131 

1,186 

7,  333 

10,  656 

4,305 

4,559 

Total                         

16,257 

In  these  two  cases  the  nitrogen  decreases  downward  until 
about  four  feet  and  below  this  depth  to  nine  feet  the 
amount  remains  nearly  constant.  It  will  be  seen  that  the 
amount  is  very  large  in  the  aggregate.  Enough  for  more 
than  240  crops  of  wheat,  40  bushels  per  acre,  could  it  all 
be  used. 

99.  Amount  of  Nitric  Acid  in  Soils. — The  amount  of  the 
available  nitrogen  in  soils,  or  nitric  acid,  is  seldom  a  large 
quantity  and  while  crops  are  growing  the  quantity  is  still 
smaller. 

Warington  states  that  the  nitric  nitrogen  in  the  soil 
seldom  reaches  5  per  cent,  of  the  total  amount  present,  and 
in  the  surface  three  feet  of  the  arable  soil  referred  to  in 
(98)  this  would  represent  36G.6  Ibs.  of  nitric  nitrogen  and 
1,650  Ibs.  of  nitric  acid  per  acre;  enough,  if  it  could  all  be 
used,  to  give  a  yield  of  211.4  bushels  of  spring  wheat  per 
acre. 


100.  Nitric  Acid  in  Fallow  Ground. — The  amount  of  ni- 
tric acid  in  fallow  ground  was  determined  to  a  depth  of  4 


Nitrogen  in  Soils. 


85 


feet  in  one-foot  sections  on  May  24  and  again  on  Aug.  22, 
and  the  results  are  given  in  the  table  below : 

Nitric  acid  in  fallow  ground  in  pounds  per  acre. 


1st  foot. 

2nd  foot. 

3rd  foot. 

4th  foot. 

If  ay  24  

78.03 

21  43 

8.13 

4  76 

293.72 

116.17 

23  50 

16  72 

215.69 

9*.  74 

15  37 

11  96 

These  figures  are  a  mean  of  the  amounts  found  in  nine 
different  sub-plots,  the  soil  being  a  clay  loam  changing  into 
sand  in  the  third  foot.  It  will  be  seen  that  the  total  amount 
of  nitric  acid  at  the  close  of  May  was  112.35  Ibs.,  contain- 
ing 24.97  Ibs.  of  nitrogen,  enough  for  only  about  14.3 
bushels  of  wheat.  On  the  22nd  of  August,  however,  there 
had  been  an  increase  to  450.11  Ibs.  per  acre,  containing 
100.02  Ibs.  of  nitrogen,  enough  for  nearly  60  bushels  of 
wheat  per  acre. 

101.  Source  of  Soil  Nitrogen — Until  recently  it  was 
maintained  that  the  nitrogen  for  the  growth  of  all  plants 
was  derived  from  the  humus  of  the  soil  and  from  the  small 
amount  of  ammonia  and  nitrous  and  nitric  acids  brought 
down  by  the  rains.  It  is  now  known  that  the  free  nitrogen 
of  the  atmosphere  is  the  ultimate  source  of  soil-nitrogen, 
and  that  the  soil-nitrogen  is  being  continually  returned  to 
the  air  again  just  as  was  long  ago  recognized  to  be  the  case 
with  the  carbon  of  living  forms. 

1.  The  immediate  source  of  humic  nitrogen  is  the  slow 
decay  of  organic  matter,  whether  this  be  the  roots,  stems  or 
leaves  of  plants  or  the  tissues  and  waste  products  of  ani- 
mals, and  a  large  part  of  the  life  processes  of  the  world 
take  place  between  the  conversion  of  humus  into  living  tis- 
sues and  dead  tissues  back  into  humus  again. 

2.  The  formation  of  nitrous  and  nitric  acids  through  an 
oxidation  of  the  nitrogen  of  the  air  by  electrical  discharges 


86 


Physics  of  the  Soil. 


such  as  occur  during  thunder  storms  is  generally  conceded. 
It  is  also  thought  that  a  part  of  these  combinations  may  be 
brought  about  through  the  action  of  ozone  upon  ammonia. 
Warington  is  also  of  the  opinion  that  the  peroxide  of  hy- 
drogen in  the  air  causes  the  conversion  of  some  atmospheric 
ammonia  into  nitric  acid,  and  hence  that  not  all  the  nitric 
acid  brought  down  by  the  rains  was  formed  as  new  ma- 
terials in  the  atmosphere  from  direct  union  of  oxygen  and 
nitrogen  gases. 

The  amount  of  nitrogen  brought  to  the  soil  with  the  rains 
seldom  equals  5  Ibs.  per  acre  per  annum  in  the  open  coun- 
try, as  shown  by  the  following  table : 

Nitrogen  as  ammonia  and  nitric  acid,  in  pounds  per  acre 
per  annum,  in  rain. 


Rothamsted. 
8  years. 

Lincoln, 
New  Zealand. 
3  years. 

Barbadoes. 
3  years. 

Lbs. 
2.53 

Lbs. 
0.74 

Lbs. 
0  93 

Nitrogen  as  nitric  acid  

0.84 

1  00 

2.84 

3.37 

1.74 

3.77 

f 

It 


FIG.  25— Showing  the  influence  of  free-nitrogen-fixing  perms  on  the  growth  of 
peas.  The  large  plants  all  grew  in  sand  containing  the  nitrogen  -fixing  bac- 
teria, while  the  small  plants  grew  in  soils  identically  the  same  except  that 
all  bacteria  were  excluded  from  them.  After  Hellriegel 


Nitrogen  in  Soils. 


87 


These  amounts,  it  will  be  seen,  are  far  too  small  to  be  of 
great  importance  to  plant  life. 

3.  The  process  of  symbiosis  is  a  third  method  by  which 
the  nitrogen  supply  of  the  soil  is  maintained  and  next  to 
the  decay  of  organic  matter  is  the  most  important  of  any 
yet  well  understood.  It  was  in  1888  that  Hellriegel  pub- 
lished the  results  of  his  studies,  which  thoroughly  estab- 
lished the  fact  that  great  numbers  of  microscopic  forms  of 
life  inhabit  the  roots  of  leguminous  plants,  forming  upon 


FIG.  26.—  Showing  the  growth  of  rye,  oats,  peas,  wheat,  flax  and  buckwheat  in 
soils  fertile  in  all  elements  of  plant  food  except  nitrogen,  and  illustrating  the 
power  of  the  pea,  through  its  root  tubercles,  to  procure  nitrogen  from  the 
air.  After  P.  Wagner. 

them  tubercles  in  which  these  organisms  live  and  withdraw 
free  nitrogen  from  the  soil-air  for  their  needs.  It  had  long 
been  known  to  farmers  that  in  some  way  clover  in  rotation 
with  other  crops  left  the  soil  richer  in  nitrogen,  and  it  is 
now  known  that  the  bacterium  which  lives  on  the  clover 
roots,  deriving  a  part  of  its  food  from  the  clover  plant,  at 
the  same  time  increases  the  nitrogen  supply  available  to  the 
clover  crop  and  so  we  have  two  forms  of  life  living  together 


Physics  of  the  Soil. 


in  what  has  been  named  symbiotic  relations.  There  are 
other  forms  of  bacteria  which  live  upon  the  bean,  pea,  lu- 
pine and  other  members  of  this  family,  also  having  the 
power  of  fixing  free  nitrogen  from  the  soil-air  in  forms 
available  to  higher  plants. 

It  is  known  that  other  forms  of  bacteria  live  in  symbiotic 
relation  with  soil  algae  and  in  this  way  increase  the  sup- 
ply of  soil  nitrogen  as  shown  by  Frank,  Schlosing,  Jr.,  and 
Laurent  in  1891,  followed  by  Kosswitsch  in  1894;  and  the 
great  demands  for  the  fixing  of  free  nitrogen  to  make  good 
the  rapid  return  of  it  to  the  air  and  loss  in  drainage  waters 
appears  to  call  for  other  agencies  than  those  named. 


i  Mi      lit' 


FIG.  27.— Showing  oats  growing  under  conditions  identical  with  those  of 
Fig.  26,  except  that  the  several  pots  received  Chile  saltpetre,  1,  2 
and  3  grams  respectively,  thus  enforcing  the  immense  importance  to 
such  plants  of  nitric  nitrogen.  After  P.  Wagner. 

4.  Winogradsky  has  shown  that  there  is  a  form  of  bacil- 
lus in  the  soil  which,  when  supplied  with  sugar  and  iso- 
lated from  the  influence  of  oxygen,  is  capable  of  thriving 
and  fixing  free  nitrogen  from  the  air,  and  this  discovery 
may  lead  to  a  knowledge  of  still  a  fourth  mode  of  increas- 
ing the  world's  supply  of  nitrogen. 


Nitrification  in  Soils.  89 

Some  of  Berthelot's  experiments  are  thought  by  him  to 
show  that  soils  destitute  of  all  visible  vegetation  may  gain 
large  quantities  of  nitrogen  when  simply  exposed  to  the  air, 
and  he  thinks  he  has  realized  gains  as  large  as  70  to  130  Ibs. 
of  nitrogen  per  acre  in  11  weeks.  Such  conclusions,  how- 
ever, require  careful  verification  as  they  are  at  least  ap- 
parently contradicted  by  field  practice. 

102.  Nitrification. — The  formation  of  nitrates  in  the  soil 
involves  at  least  four  distinct  phases  or  stages :  (1 }  llio  ain- 
monia   stage,-  (2)  the  nitrous   acid   stage,  (3)  the   nitric 
acid  stage    and    (4)    the    nitrate  forming  stage.     When 
humus  or  dead  organic  matter  is  placed  under  the  right 
conditions  of  temperature,  moisture  and  air  in  the  pres- 
ence of  ammonia-forming  germs,   these  organisms  feed 
upon  portions  of  it  and  throw  off  ammonia  as  a  waste  prod- 
uct.    Ammonia  is  extremely  soluble  in  water  and  is  re- 
tained by  it   in  large   volumes.     Even   dry   soil    has  the 
power  of  condensing  and  retaining  it.     In  a  fertile  soil 
where  ammonia  has  been  formed  there  are  also  present 
nitrous  acid  germs  which  are  able  to  use  ammonia  in  their 
life  processes  but  throwing  off  nitrous  acid  as  a  waste  prod- 
uct.    The  niter  germs  or  "mother  of  petre"  utilize  the 
nitrous  acid  in  their  work  and  throw  off  as  a  by-product 
nitric  acid.     This  nitric  acid  readily  attacks  any  of  the 
bases  in  the  soil  which  are  held  by  carbonic  and  other  weak 
acids,  displacing  them  and  forming  nitrate  of  lime,  mag- 
nesia, potash  or  soda,  as  the  case  may  be. 

In  the  old  days  of  "niter  farming,"  when  nitrate  of 
potash  for  gunpowder  was  obtained  from  the  soil,  great 
pains  were  taken  to  form  a  soil  rich  in  organic  matter  and 
to  keep  it  warm,  well  supplied  with  moisture  and  thor- 
oughly aerated.  These,  too,  are  the  points  to  be  secured  in 
the  best  management  of  soil  for  farm  and  garden  crops. 

103.  Denitrification. — Pitted  against  the  processes  of  fix- 
ing free  nitrogen  from  the  air,  which  have  been  described, 


90  Physics  of  the  Soil. 

there  are  other  processes  which  reverse  these  operations  and 
set  free  again  the  nitrogen  of  organic  compounds  and  of  ni- 
trates so  that  it  is  again  returned  to  the  atmosphere  as  free 
nitrogen  gas. 

(1)  Dr.  Angus  Smith  showed  in  1867  that  nitrates  in 
sewage  waters  are  decomposed  and  the  nitrogen  set  free 
as  a  gas.  (2)  Scblosing  showed  that  when  moist  humus- 
bearing  soils  are  placed  in  an  atmosphere  free  from  oxygen 
they  quickly  lose  all  traces  of  nitrates.  (3)  Warington 
demonstrated  that  sodium  nitrate  in  a  water-logged  soil 
is  decomposed  and  the  nitrogen  liberated  as  a  gas.  (4) 
So  great  is  the  demand  for  oxygen  in  rich  water-logged 
soils  that  according  to  the  experiments  of  Mtintz  even  such 
compounds  as  chlorates,  iodates  and  bromates  are  deprived 
of  their  oxygen,  leaving  iodides,  chlorides  and  bromides  in 
their  place.  (5)  When  black  marsh  soils  are  stirred  up 
with  water  and  allowed  to  stand  Prof.  J.  A.  Jeffery  and  the 
writer  have  shown  that  the  nitrates  rapidly  disappear  and 
nitrogen  gas  is  set  free. 

In  all  of  these  cases  there  are  microscopic  organisms  in 
the  soil  and  water  whose  needs  for  oxygen  are  so  great  that 
when  that  which  is  free  in  the  soil-air  or  water-air  is  not 
sufficient  they  have  the  power  of  decomposing  nitrates  and 
even  some  organic  compounds  for  the  oxygen  they  contain 
and  in  this  way  liberate  free  nitrogen. 

(6)  There  is  still  another  condition  under  which  denitri- 
fication  takes  place  in  which  the  loss  is  large,  rapid  and 
nearly  complete.  It  is  when  human  excrements  are  covered 
with  pulverized  dry  soil,  as  is  done  in  the  dry-earth  closets. 
The  late  Colonel  Waring  kept  two  tons  of  dry  earth  for  a 
number  of  years,  having  it  used  over  and  over  again  in  or- 
der to  see  how  long  it  might  be  used  without  losing  its  effi- 
ciency. The  closets  were  filled  with  the  dry  earth  and  excre- 
ment about  6  times  each  year,  and  when  they  were  emptied 
the  material  was  thrown  in  a  heap  on  a  floor  of  a  well  venti- 
lated cellar  to  dry.  After  the  same  soil  had  been  used  over 
not  less  than  10  times  it  was  analyzed  for  the  amount  of 
nitrogen  it  contained,  and  in  4,000  Ibs.  of  the  soil  was  found 


Denitrifi cation  of  Soils,  91 

no  more  than  11  Ibs.  of  nitrogen  and  yet  not  less  than  230 
Ibs.  had  been  added  to  it  and  the  soil  at  the  start  contained 
at  least  3  Ibs.  There  had  been  set  free  therefore 

230  —  8  =  222  Ibs.  of  nitrogen. 

Nor  was  this  all,  for  so  completely  had  all  the  carbonaceous 
materials  been  oxidized  that  even  the  paper  used  had  en- 
tirely disappeared. 

How  far  these  processes  take  place  under  field  condi- 
tions when  farmyard  manure  is  applied  we  have  yet  to 
learn. 


CHAPTER  III. 
SOLUBLE   SALTS  IN  FIELD   SOILS. 

All  the  food  of  plants  is  taken  by  them  in  the  form  of 
liquids  or  of  gases,  and  hence  the  fertility  of  a  soil  must  be 
determined  by  the  rate  at  which  plant  food  may  be  dis- 
solved in  the  soil  water  and  carried  to  them  at  the  time  the 
crops  are  growing.  If  the  ash  ingredients  and  the  nitro- 
gen used  by  plants  while  growing  are  supplied  in  the  soil 
water  as  rapidly  as  the  crop  can  use  them,  then  maximum 
yields  will  be  certain  if  the  temperature  and  sunshine  are 
nlso  right. 

1C4.  Amount  of  Soluble  Salts  in  Field  Soils. — There  is  a 
very  wide  difference  in  the  amount  of  salts  dissolved  in 
soil  water  under  different  conditions.  In  arid  regions, 
where  there  is  little  soil  leaching,  the  salts  become  in  places 
so  abundant  that  plants  are  unable  to  grow  and  alkali 
lands  are  the  result.  In  humid  climates,  especially  where 
the  soils  are  sandy,  the  salts  may  be  so  small  in  amount 
that  plants  starve.  In  the  table  below  these  differences 
are  shown  for  the  surface  foot. 


Watersolnble  salts  in  soils 
of  arid  climates. 

Water  soluble  salts  in  soils 
of  humid  climates. 

Where  bar- 
ley will  not 
grow. 

Whore  bar- 
ley prows 
4ft.  hi«li. 

Fertile  clay 
loam. 

Poor  sandy 
soil. 

21 

81 

Lbs.  per  million  of  dry  soil 
LJv.  per  acre  of  4,000,000 
Ibs  

8,585 
34,340 

4.877 
15,503 

272 
1,088 

These  figures  show  a  range  of  total  salts  soluble  in  water 
from  17  tons  per  acre  foot  to  less  than  .05  tons. 


Soluble  Salts  in  Soils. 


93 


105.  Maximum  Amount   of  Water   Soluble   Salts   Which 
Limit  Plant  Growth. — Hilgard  concludes  from  his  studies 
that  the  maximum  amount  of  soluble  alkali  salts  which  are 
consistent  with   a   full   crop   of  barley   hay    is  25,000  to 
32,000  Ibs.  per  acre  in  the  surface  four  feet  of  soil,  pro- 
vided this  is  not  more  than  one-half  its  weight  sodium  car- 
bonate. 

Whitney  places  the  limit  of  possible  plant  production 
in  the  soils  of  the  Yellowstone  Park  at  15,000  Ibs.  per 
acre  in  the  surface  foot,  where  the  black  alkali  or  sodium 
carbonate  is  absent. 

Grapes  grow  in  Algeria  in  alkali  soils  containing  600 
Ibs.  per  million  of  dry  soil  but  die  when  it  reaches  1,YOO 
Ibs.  per  million  in  the  surface  soil  and  3,700  in  the  sub- 
soil ;  but  grain  crops  grow  normally  when  the  soil  contains 
2,000  Ibs.  per  million. 

106.  Why  too  Much  Soluble  Salt  in  Soil  Kills  Plants. — De 

Vries  found,  as  represented  in  Fig.  28,  that  when  the  liv- 


Fto.  28.— Showing  the  effect  of  too  strong  solution  of  salts  on  the  proto- 
plasm of  plant  cells. 

ing  cells  of  a  plant  were  immersed  in  a  4  per  cent,  solution 
of  potassium  nitrate,  there  was  first  a  shrinkage  in  volume 
through  a  loss  of  water,  as  shown  between  1  and  2.  When 
the  solution  was  given  a  strength  of  6  per  cent,  the  proto- 


94  Physics  of  the  Soil. 

plasmic  lining,  p,  began  to  shrink  away  from  the  cell  wall 
h,  as  shown  at  3,  and  when  the  strength  of  the  solution  was 
made  10  per  cent.,  the  conditions  shown  in  4  are  produced. 
When  the  cells  of  plants  are  affected  in  this  way  they  wilt 
and  growth  ceases. 

A  soil  containing  20  per  cent,  of  water  and  also  2,000 
Ibs.  of  water  soluble  salts  per  million  of  dry  soil  would 
contain  2,000  Ibs.  in  200,000  Ibs.  of  water,  or  1  part  in  100, 
which  is  1  per  cent.  If  the  soluble  salts  constitute  2  per 
cent,  of  the  dry  weight  of  the  soil  then  with  20  per  cent,  of 
moisture  present  the  strength  of  the  soil  solution  would  be 
equal  to  that  which  De  Vries  found  fatal  to  plants,  or  10 
per  cent. 

The  salts  in  the  surface  three  inches  of  soil  upon  which 
Hilgard  found  barley  to  grow  four  feet  high  were  1.2  per 
cent,  while  they  were  2. 44 per  cent,  in  the  same  level  where 
the  barley  died.  With  20  per  cent,  of  moisture  in  the  soil, 
and  all  the  salts  dissolved,  the  soil  solution  in  the  first 
case  would  represent  a  strength  of  6  per  cent,  and  in  the 
second  case  12.2  per  cent.,  which  is  larger  than  the  amount 
De  Vries  found  fatal. 

107.  Concentration  of  Salts  in  Zones. — Where  long  contin- 
ued drought  has  occurred  in  soils  rich  in  soluble  salts  the 
tendency  is  for  the  salts  to  collect  in  the  surface  two  or 
three  inches  and  in  this  way  become  injurious  to  plants 
when  they  would  not  be  so  with  an  abundance  of  water  in 
the  soil. 

When  heavy  rains  follow  such  a  concentration  of  salts 
at  the  surface,  or  if  the  land  is  irrigated  so  as  to  produce 
percolation,  the  result  is  to  wash  the  salts  down  in  a  body 
to  the  depth  reached  by  percolation,  and  hence  it  may  hap- 
pen that  a  layer  of  soil  very  rich  in  salts  may  occur  at  the 
surface  at  one  time  and  later  at  a  distance  of  12,  18,  24  or 
30  or  more  inches  below,  determined  by  the  depth  of  per- 
colation. 

108.  Origin  of  Soluble  Salts — The  excessive  amounts  of 
salts  found  in  alkali  lands  are  usually  the  result  of  long 


Soluble  Salts  in  Soils.  95 

continued  rock  decay  under  conditions  where  little  or  no 
leaching  has  taken  place.  Rains  enough  fall  to  produce 
decay,  but  not  enough  to  carry  the  salts  formed  into  the 
drainage  channels  and  out  of  the  country.  This  is  why 
alkali  lands  are  largely  peculiar  to  desert  or  semi-arid 
climates. 

109.  Leaching  Necessary    to  Fertile  Soils. — It    is    clear 
from  106  and  108  that  if  there  was  not  some  leaching  to 
take  up  and  carry  away  the  extremely  soluble  salts  not 
available  as  plant  food  all  soils  would  in  time  become  "al- 
kali lands ;"  so  that  while  excessive  leaching  is  undesirable, 
a  sufficient  amount  is  indispensable. 

The  prevention  of  the  accumulation  of  undesirable  solu- 
ble salts  in  the  soil  of  irrigated  lands  in  dry  climates  is  one 
of  the  most  serious  of  practical  problems. 

110.  Soluble  Salts  in  Marsh  Soils. — The  black  marsh  soils 
of  humid  climates  often  contain  unusually  large  amounts 
of  soluble  salts,  sometimes  reaching  2,366  parts  per  mil- 
lion of  the  dry  soil  in  the  surface  6  inches  after  maturing 
a  crop.     This  would  make  the  water  contain  1.18  per  cent, 
of  salts  if  the  water  content  of  the  soil  was  20  Ibs.  per  100 
of  dry  soil.     Many  of  these  soils  behave  much  like  alkali 
lands,  being   unproductive,  the   crops   often   dying  when 
there  is  no  evident  reason  for  it. 

111.  Correction  for  Alkali  Lands. — It  has  been  found  that 
when  a  soil  is  unproductive  from  too  high  a  per  cent,  of 
sodium  carbonate  or  black  alkali  and  there  is  not  enough 
of  other  soluble  salts  to  be  injurious,  this  may  be  corrected 
in  part  by  the  use  of  gypsum,  or  land  plaster,  which  has  the 
effect  of  converting  the  carbonate  into  the  sulphate  or 
"white  alkali,"  like  amounts  of  which  are  less  harmful. 

It  often  happens  that  waters  which  must  be  used  in  irri- 
gation contain  black  alkali,  and  where  this  is  the  case  it  is 
well  to  correct  the  water  by  using  land  plaster  in  the  reser- 
voirs or  distributing  canals,  for  the  water  to  run  over  or 
through,  before  reaching  the  field. 


96 


Physics  of  the  Soil. 


FIG, 


29. — Showing  the  seasonal  changes  in  tho  amounts  of  nitrates  in  each  of  the 
surface  four  feet  of  .soil  under  growing  corn. 


Soluble  Salts  in  Soils. 


97 


FIG.  30.— Showing  the  seasonal  chnnges  In  the  amounts  of  soluble  salts 
in   the  soil   under  growing  corn. 


98  Physics  of  the  Soil. 

112.  Drainage  the  Ultimate  Remedy. — Drainage  must  be 
the  ultimate  remedy  for  any  alkali  land,  as  it  can  be  only 
a  matter  of  time  when  any  fertile  soil  will  develop  enough 
undesirable  soluble  salts  to  render  it  sterile  or  less  produc- 
tive, unless  the  soluble  salts  not  needed  are  removed,  and 
only  drainage  can  do  this. 

113.  Deep  and  Frequent  Tillage  Helpful. — It  is  clear  that 
whatever  means  will  prevent  the  excessive  evaporation  of 
water  from  the  surface  will  in  so  far  lessen  the  concentra- 
tion of  salts  there,  and  hence  frequent  and  deep  cultiva- 
tion,   to  form   effective  mulches,    will   lessen   the   rise  of 
water,  and  therefore  of  salts,  to  the  surface  and  in  this  way 
permit  crops  to  be  grown  on  soils  which  are  critically  near 
the  limit  of  sterility  on  account  of  the  high  salt  content. 

114.  Change  in  Soluble  Salts  with  Season. — In  Figs.  29 
and  30  are  represented  the  changes  in  the  nitrates  and  total 
soluble  salts  in  the  surface  four  feet  under  three  fields  of 
corn,  beginning  with  April  and  ending  with  Sept.     Re- 
ferring to  the  nitrate  curves  it  will  be  seen  that  the  nitrates 
start  in  April  nearly  equal  in  the  four  feet,  but  increase 
rapidly  in  the  first  foot  until  the  middle  of  June,  when 
the  corn  begins  to  draw  on  the  supply.     From  this  time 
they  decrease  rapidly  until  the  middle  of  July,  when  they 
are  less  than  in  April  and  less  than  in  the  second  foot.     By 
the  middle  of  August,  when  the  crop  has  ceased  to  draw 
much  but  water  from  the  soil,  there  is  a  slow  increase  again 
and  then  one  more  rapid  after  the  corn  is  cut,  Sept.  1. 

The  change  in  the  total  salts  is  much  less  marked,  but 
evident,  there  being  a  general  decrease.  The  mean  amount 
of  salts  at  the  beginning  and  at  the  end  of  the  season  are : 

April  18.  Sept.  1. 

Total  salts 540  363 

Nitrates 86  32 

Difference 454  331 

From  these  figures  it  appears  that  the  salts,  other  than 
nitrates,  have  decreased  during  the  season  123  Ibs.  per  mil- 
lion of  the  dry  soil  for  the  four  feet,  or  1,968  lb$, 


Soluble  Salts  in  Soils. 


99 


115.  Variation  of  Soluble  Salts  with  Different  Crops. — . 
There  is  a  marked  difference  in  the  amount  of  soluble  salts, 
and  especially  in  the  amount  of  nitrates,  in  soils  under 
crops  like  corn  and  potatoes,  where  inter-tillage  is  prac- 
ticed, and  under  such  crops  as  clover  and  oats,  where  the 
ground  is  not  cultivated  at  any  time  of  the  season.  This 
is  very  clearly  shown  in  Fig.  32 ;  the  nitrates  are  plotted 
in  the  lower  two  sets  of  curves  and  the  total  soluble  salts 
in  the  upper  two  sets. 

The  nitrates  in  the  first  foot  under  the  corn  and  potatoes 
increased  rapidly  until  July  1st,  when  they  were  five  times 
as  concentrated  as  in  the  fourth  foot ;  but  in  30  days  more 
the  nitrates  had  been  reduced  from  over  400  Ibs.  to  40  Ibs. 
per  acre. 


PARTS  PER  MILLION  <     DRY  SOIL. 


FIG.  31.— Sliows  the  menu  amount  of  nitrates  and  total  soluble  salts 
in  the  surface  four  feet  of  soil  under  cultivated  and  not  cultivated 
crops.  Heavy  shading  is  uncultivated  ground. 

In  the  case  of  the  uncultivated  crops  the  fields  started 
with  about  40  Ibs.  per  acre  and  increased  to  only  70,  June 
1st,  when  they  were  highest;  from  this  date  they  fell  to 
little  more  than  10  Ibs.  per  acre  in  the  surface  foot,  but 
rose  again  to  60  Ibs.  at  the  end  of  August. 

With  the  total  soluble  salts  there  was  at  first  a  more 


Physics  of  the  Soil. 


GROuND    NOT  CULTIVATED 


GROUND    CULTIVATED 

CORN  AND   POTATOES 


Fin.   32.— Showing   the   difference   between    the   amounts   of   nitrates   and 
of  total  soluble  salts  in  the  soil  under  cultivated  and   not  cultivated 
crops. 


Closeness  of  Plant  Feeding.  101 

rapid  rise,  from  nearly  300  Ibs.  per  acre  in  the  surface  foot 
on  the  cultivated  ground  April  18,  to  about  500  Ibs.  per 
acre,  but  falling  again  on  August  1st  to  250  Ibs. 

On  the  clover  plots  the  start  was  at  250  Jbs.  per  acre  in 
the  surface  foot,  rising  to  290  Ibs.  in  12  days.  From  this 
date  there  was  a  slow  decrease,  falling  to  220  Ibs.  on  the 
date  when  the  cultivated  grounds  were  highest,  at  GOO  Ibs. 
per  acre. 

116.  Relation  Between  Nitrates  and  Total  Soluble  Salts — . 
As  a  general  rule  when  the  nitric  nitrogen  in  clay  loams 
is  very  high  the  total  soluble  salts,  as  indicated  by  the 
electrical  method,  are  very  low.     It  will  even  happen  that 
the  electrical  resistance  will  show  but  little  more  salts  than 
are  required  to  account  for  the  nitrates,  and  this  is  perhaps 
what  should  be  expected  for,  if  nitric  acid  is  being  formed 
in  the  presence  of  carbonates,  these  would  be  decomposed 
to  form  nitrates,  and  if  the  rate  of  nitrification  were  suf- 
ficiently rapid,  it  might  be  that  all  the  carbonates  would  be 
decomposed  and  little  else  but  nitrates  left. 

The  ratio  of  total  soluble  salts  to  nitrates  in  the  surface 
foot  of  the  five  cultivated  fields  represented  by  the  curves 
was  a  mean  for  the  season  of  2.14  to  1,  while  in  the  surface 
foot  of  the  clover  fields  it  was  4.8  to  1. 

For  the  second,  third  and  fourth  feet  the  ratio  is  Y.29  to 
1  for  the  corn  and  potatoes,  and  9.97  to  1  for  the  clover, 
alfalfa  and  oats ;  and  these  ratios  are  what  would  be  ex- 
pected if  the  formation  of  nitric  acid  destroys  the  carbon- 
ates and  bi-carbonates  in  the  soil  water. 

117.  Closeness  of  Plant  Feeding — It  was  pointed  out.  in 
(7)  what  small  amounts  of  a  fertilizer  can  be  widely  dis- 
tributed through  an  acre  of  soil,  and  we  may  now  consider 
how  extremely  close  plants  do  feed  the  nitrates  of  a  soil. 
In  the  table  which  follows  are  given  the  amounts  of  ni- 
trates which  were  found  in  each  foot  of  nine  field  plots, 
represented  by  the  curves,  between  July  18  and  Sept.  1. 

7 


BIO-AGRICULTURAL  LIBRA! 
UNIVERSITY  OF  CALIFORNI 


102 


Physics  of  the  Soil. 


Tablet  showing  mean  amounts  of  nitrates  under  different  crops 
between  July  18  and  Sept.  1,  in  Ibs.  per  acre  of  dry  soil. 


Plotl. 

Plot  2. 

PlotG. 

Plot  4. 

PlotS. 

Plot  6. 

Plot  7. 

Plot  8. 

Plot  9. 

Corn. 

Clover. 

Corn. 

Oats 
and 
clover. 

Pota 
toes. 

Pota- 
toes. 

Clover. 

Alfalfa 

Corn. 

1st  foot.. 
2nd  foot. 
3rd  foot.. 

4t!i  i.M.t-. 

Lbs. 
50.94 
127.35 
83.52 
40.83 

Lbs. 
58.32 
23.74 
10.2-5 
14.80 

Lbs. 
24.11 

4X.81 
59.44 
64.82 

Lbs. 
15.07 
It.  42 

18.81 
27.05 

Lbs. 
130.21 
155  !  5 
49.65 
21.08 

Lbs. 
10V32 
172  62 
50.  f  6 
59.82 

Lbs. 
44.91 
15  63 
1.75 
4.59 

Lbs. 

18  t-4 
10.6.1 
9.53 
9.73 

Lbs. 
10.85 
8  S3 
10.79 
12  51 

\Vhen  these  amounts  are  expressed  as  parts  per  million 
of  the  dry  soil  in  the  form  of  nitrogen,  they  stand  3.38, 
1.61,  0.72  for  corn;  3.87,  2.98,  1.00  for  clover;  1.25  for 
alfalfa  and  6.99  for  potatoes,  and  yet  with  these  small 
amounts  of  nitrogen  in  the  soil  during  the  time  when  the 
chief  growth  was  being  made,  large  yields  were  produced. 

118.  Limits  of  Nitric  Nitrogen  at  Which  Corn  and  Oats 
Turn  Yellow. — Taking  samples  of  soil  from  the  surface 
foot  upon  which  oats  were  turning  yellow  and  under  adja- 
cent areas  where  the  plants  were  normal  green  it  was  found 
that  two  sets  of  duplicate  determinations  gave 

Oats  yellow       Oatj  green. 
(  June  10    .025  .213 

Parts  of  nitric  nitrogen  per  million  of  dry  soil —  < 

(June  11     .027  .297 

These  amounts,  when  expressed  in  pounds  per  acre  and 
as  nitrates,  are  only  .392  Ibs.  and  3.843  Ibs.,  respectively, 
for  the  yellow  and  green  oats. 

Table  showing  the  amounts  of  nitric  nitrogen  under  corn  row* 
where  leaves  are  turning  yellow  and  where  they  are  yet 
normal  green. 


Depth. 

Plot  9. 

Marsh  soil. 

Randall  field. 

Yellow. 

Green. 

Yellow. 

Green. 

Yellow. 

Green. 

1st  foot  

0.61 
0  14 
0.41 
0.42 

0.92 
1.70 
2.95 
1.82 

0.95 
0.40 
0.07 
0.00 

3.62 
1.41 
0.52 
0.00 

0.10 
0.06 
0.25 
0.30 

0.95 
0.60 
0.37 
0.30 

2nd  foot  

3rd  foot  

4tb  foot  

\Nitrales  in  Soils. 


103 


Small  as  these  amounts  of  nitric  nitrogen  are  the  yield 
of  corn  on  plot  9  was  a  mean  of  8,000  Ibs.  of  water-free 
matter  per  acre.  On  another  plot  where  the  yield  was 
11,440  Ibs.  of  water-free  matter  per  acre  the  nitric  nitro- 
gen was  reduced  as  low  as  1.44G  parts  per  million  in  the 
first  foot  and  .726  parts  in  the  second  foot. 

It  must  be  understood  that^in  these  cases  the  demands 
for  nitrogen  were  so  urgent  that  the  plants  were  taking  it 
up  almost  as  rapidly  as  it  could  be  produced,  leaving  the 
amounts  so  low,  as  the  figures  show. 

119.  Nitrates  of  Fallow  and  Cropped  Ground. — In  the 
table  which  follows  are  given  the  amounts  of  nitrates 
found  under  different  crops  and,  at  the  same  time,  under 
immediately  adjacent  fallow  ground  which  had  been  cul- 
tivated and  kept  free  from  weeds. 


- 

Oats. 

Fallow. 

Barley. 

Nitrates. 

Total 
salts. 

Nitrates. 

Total 
salts. 

Nitrates 

Total 
salts. 

1st   foot  

5.94 
8.12 
4.73 
4.60 

Oa 

3.25 
3.22 

2  Ho 

70.94 
114.6 
124.7 
39.44 

ts. 

80.35 
162.1 
102.7 

58.24 

ts. 

78.56 
10*.  9 
72.98 
33.99 

246.40 
26.75 
6.50 
2.84 

Fal 

143.05 
*9.50 
8.87 
4.10 

Fall 

129.15 
35.60 
9.11 
4.08 

199.3 
123.5 
108.0 
42.10 

ow. 

206.1 
254.3 
115.0 
95.32 

ow. 

211.3 

254  7 
117.8 
61.92 

2.62 
5.10 
4  04 
3.03 

Pe 

8.38 
18.57 
6.59 
2.66 

Sprin 

1.24 
2.62 
2.07 
2.78 

61.72 
87.08 
112.6 
51.76 

as. 

77.00 
197.2 
135.8 
44.62 

?  rye. 

77.34 
102.1 

94.82 
48.85 

2d    foot  

3d    foot  

4th  foot  

1st  foot  

2d    foot  

3d    foot  

4th  foot  

2.70 
Oa 

2.47 

2.46 
3.  S3 
3.16 

1st  foot  

2d    foot  

3d    foot  

4th  foot  

If  the  mean  amount  of  nitrates  in  the  surface  foot  of  the 
fallow  ground  and  under  the  crops  are  expressed  in  pounds 
per  acre  they  stand  473.65  to  10.88.  This  difference  is 
enough  for  85  bushels  of  oats  per  acre,  where  the  ratio  of 
grain  to  straw  stands  as  3  to  5. 


104: 


Physics  of  the  Soil. 


120.  Loss  of  Nitrates  from  Fallow  Ground  During  Winter 
and  Spring. — A  field  which  has  been  kept  fallow  during  a 
whole  season  and  cultivated  either  once  per  week  or  once  in 
two  weeks  had  the  nitrates  determined  in  it  on  August  25 
and  again  the  next  spring,  April  30.  The  field  was  di- 
vided into  nine  plots  and  the  nitric  nitrogen  was  deter- 
mined in  each  one  to  a  depth  of  four  feet  on  both  dates. 
The  results  are  given  in  the  next  table. 

Table  showing  the  amount  of  nitric  nitrogen  found  in  fallow 
ground  after  the  leaching  of  winter  and  early  spring. 
Pounds  per  million  of  dry  soil. 


No.  of  plot. 

I. 

2. 

3. 

4-. 

5. 

6. 

7. 

8. 

9. 

Apr.  30,  1900  ( 

75.90 

58.31 

58.05 

55.22 

51  68 

51.25 

38.02 

44.34 

48.26 

Aug.  22,  l-9.fi 

16.81 

13.58 

26.67 

26.  M) 

19.0.4 

16.82 

5.50 

24  07 

19.60 

2d  foot  \ 

Apr.   30,  190.)  \ 

15.81 

16.75 

7.97 

6.51 

13  06 

15.66 

17.33 

18.56 

14.85 

Aug.  22,  18'.->9  I 

4.34 

7.75 

1.81 

9.07 

5.74 

2.76 

1.43 

6.06 

6.61 

8d  footj 

Apr.   30,  ItOO  ( 
Aug.  22,  1S99  ( 

2.46 
.70 

4.75 
.54 

4.93 
2.4i 

4.89 
.80 

3.94 
0.54 

7.35 
1.37 

6.04 
0.95 

8.24 
0.54 

6.71 
3  01 

4thfoot  ] 

Apr.  30,  1900  ] 
Aug.  22,  1S99  1 

2.95 

2.37 

3.05 
1  04 

2.35 

2.01 
1  P5 

2.36 
0  52 

3.65 
0  26 

5.60 
0  53 

5.08 
'•t  51 

It  is  clear  from  this  table  that  however  large  the  leach- 
ing may  have  been  it  was  not  enough  to  prevent  the  nitrates 


FIG.  33.— Showing  the  difference  in  the  amount  of  nitrates  in  the  surfnco 
four  feet  of  fallow  ground,  the  succeeding  spring,  aiid  that  upon  which 
crops  had  been  grown. 


Nitrates  in  Soils. 


105 


being  higher  the  following  May  than  they  were  August  22 
before. 

121.  Nitrates  on  Fallow  Ground  in  Spring  Compared  with 
That  not  Fallow. — Comparing  the  mean  amount  of  nitric 
nitrogen  in  nine  field  plots  bearing  crops  in  1899  with  that 
of  the  nine  fallow  plots  of  the  same  year,  as  found  in  the 
spring  of  1900,  the  amounts  are  as  stated  in  the  table  below 
and  represented  graphically  in  Fig.  33. 

Table  showing  the  difference*  in  the  amounts  of  nitric  nitro- 
gen after  the  winter  and  early  spring  rains  in  ground  kept 
fallow  and  free  from  iveeds  the  previous  season  and  that 
bearing  crops. 


Depth. 

1st  foot. 

2d  foot. 

3rd  foot. 

4th  foot. 

Fallow  plots,  pounds  per  acre.. 

212.00 

56.22 

21.91 

13.11 

Plots  not  fallow,  pounds  per  acre 

25.24 

1503 

10.00 

7.24 

Difference  

183.76 

41  14 

11  91 

5.87 

From  this  it  is  clear  that  the  crops  on  the  fallow  ground 
start  out  in  the  spring  under  conditions  very  superior  to 
those  on  the  fields  which  had  not  been  fallow,  there  being 
245.68  Ibs.  of  nitrates  more  per  acre  in  the  surface  four 
feet. 

122.  Development  of  Nitrates  Influenced  by  Depth  and 
Frequency  of  Cultivation. — When  a  series  of  cylinders  like 
those  represented  in  Fig.  58,  p.  187,  are  mulched  by  stir- 
ring at  different  depths  and  the  stirring  is  repeated  at  dif- 
ferent intervals  the  rate  of  formation  of  nitrates  is  ma- 
terially modified,  as  shown  in  the  table  below: 

Difference  in  the  amount  of  nitric  nitrogen,  after  258  days,  due 
.  to  differences  in  depth  and  frequency  of  cultivation. 


Depth  of  cultivati'n. 

Cultivated  once  per  week. 

Cultivated  once  in  two  weeks. 

1  inch  deep  

Lbs.  per  acre. 
217.69 

Lbs.  per  acre. 
213  29 

2  inches  deep  

323.44 

199  00 

3  inches  deep  

441.24 

401.68 

4  inches  deep... 

3b7.96 

245.26 

106  Physics  of  the  Soil. 

It  can  be  seen  that  the  nitric  nitrogen  has  increased  in 
both  series  to  a  depth  of  3-inch  cultivation  and  it  has  in- 
creased with  the  frequency  of  the  cultivation. 

123.  Soluble  Salts  Affect  the  Movement  of  Soil  Moisture 

The  varying  strength  of  salt  solutions  in  soil  moisture  mod- 
ify both  the  movement  of  moisture  in  the  soil  and  its  rate 
of  loss  from  the  surface.     These  movements  are  influenced 
(1)  by  changes  in  the  intensity  of  surface  tension;   (2) 
l>y  changes  in  the  internal  friction  of  the  soil  moisture  or 
its  viscosity;  and  (3)  by  modifications  of  the  surface  of 
the  soil  due  to  deposits  of  salts  upon  and  within  it,  where 
evaporation  is  taking  place. 

124.  Modification  of  Surface  Tension  by  Soluble  Salts. — 
As  a  general  rule  the  surface  tension  of  a  strong  soil  solu- 
tion is  greater  than  that  of  a  weaker  one,  or  of  pure  water, 
and  in  so  far  as  this  influence  is  operative  it  tends  to  in- 
crease the  rate  of  capillary  movement  toward  the  surface 
or  toward  the  roots  of  plants. 

125.  Salts  in  Solution  Lessen  Rate  cf  Evaporation. — When 
water  has  been  brought  to  the  surface  of  the  soil  by  capil- 
larity it  has  yet  to  evaporate  and  unless  this  takes  place  the 
surface  soil  would  become  capillarily  saturated  with  water 
and  remain  so.     Since  salts  in  solution  increase  the  sur- 
face tension  it  will  require  a  greater  energy — a  higher 
temperature — to  throw  the  water  molecules  off  into  the  air 
than  would  be  required  to  do  so  from  the  surface  of  pure 
water  and  hence  the  evaporation  from  soil  solutions  rich 
in  salts  is  slower  than  it  is  from  weaker  ones  under  other- 
wise like  conditions.     As  the  salts  become  concentrated  at 
the  surface  by  evaporation  the  moisture  becomes  a  stronger 
and  stronger  solution  and  hence  the  rate  of  evaporation  be- 
comes less  and  less  so  far  as  it  can  be  influenced  by  this 
factor,  in  this  way. 

126.  Viscosity  of  Soil  Water  Modified  by  Soluble  Salts. — 
The  internal  friction  of  soil  moisture  is  made  greater  by 


Physical  Effects  of  Soluble  Salts.  107 

the  presence  of  salts  in  solution  and  the  more  concentrated 
the  soil  solution  is  the  greater  is  the  internal  friction,  and 
hence  the  slower  must  be  the  rate  of  flow,  and  it  may  be  that 
the  much  slower  rate  of  capillary  movement  in  a  compara- 
tively dry  soil  is  to  a  considerable  extent  due  to  this  in- 
creased viscosity  or  internal  friction.  But  as  one  effect  of 
the  salt  in  solution  is  to  increase  the  surface  tension,  while 
the  other  decreases  the  flow  by  increasing  the  friction,  the 
two  influences  work  against  each  other,  making  the  com- 
bined result  less  than  it  would  be  could  either  act  alone. 

127.  Deposits  of  Salts  after  Evaporation  May  Lessen  Loss 
of  Soil  Moisture — Where  water  rich  in  salts  is  being  evap- 
orated from  a  soil  these  salts  may  accumulate  upon  the  sur- 
face and  form  a  sort  of  mulch  more  or  less  effective  accord- 
ing to  its  texture ;  or  they  may  be  deposited  as  a  crust  upon, 
over  and  between  the  soil  grains,  which  may  nearly  close 
the  capillary  pores  and  in  this  way  lessen  the  loss  of  water 
by  evaporation.  Such  a  closing  of  the  pores  is  likely  to  be 
more  harmful  in  shutting  out  the  air  and  in  lessening  the 
freedom  of  entrance  of  water  after  rains  than  it  can  render 
resistance  in  conserving  soil  moisture. 


CHAPTER  IV. 
PHYSICAL  NATURE  OF  SOILS. 

128.  Texture  of  Soils. — The  size  of  soil  grains  and  the 
way  they  are  grouped  in  composite  clusters  forming  ker- 
nels or  crumbs  has  a  very  great  influence  in  determining 
the  physical  properties  of  soils  and  their  agricultural  value, 
and  as  soils  vary  quite  as  widely  in  the  size  and  arrange- 
ment of  their  grains  as  they  do  in  their  chemical  composi- 
tion it  is  clear  that  this  phase  of  soil  problems  must  take  at 
least  equal  rank  with  those  considered  in  the  last  chapter. 

In  all  agricultural  soils  except  the  very  coarse  and  sandy 
ones  there  is  a  composite  granular  structure  which  renders 
them  much  more  open  and  porous  than  they  could  otherwise 
be,  and  when  a  soil  is  puddled  this  structure  or  texture  is 
destroyed  in  a  large  measure  and  the  separate  grains  are 
then  brought  into  the  closest  possible  arrangement,  and 
they  become  nearly  or  quite  impervious  to  both  water  and 
air,  approaching  the  condition  of  brick  and  potter's  clays. 

129.  Size  of  Soil  Grains. — When  the  fragments  of  rock  are 
so  coarse  that  very  few  are  smaller  than  .01  of  an  inch  in 
diameter  we  have  a  sand  rather  than  a  soil.  Most  plas- 
tering sands  are  made  up  of  grains  ranging  from  .01  up  to 
.08  of  an  inch  in  diameter. 

In  the  table  which  follows  is  given  the  mechanical  anal- 
yses of  three  types  of  soil : 

It  will  be  seen  from  this  table  that  only  .8  per  cent,  of 
either  soil  is  made  up  of  grains  having  diameters  so  great 
that  only  23  are  required  to  span  a  linear  inch,  while  the 
heavy  clay  soil  has  nearly  one-half  of  its  weight  made  up 


Texture  of  Soils. 


109 


of  grains  so  small  that  25,000  of  them  must  be  placed  side 
by  side  to  span  a  linear  inch. 


SANDY  SOIL. 

LOESS  SOIL. 

HEAVY  CLAY  SOIL. 

Number  of 

Number  of 

Number  of 

Diana. 

m.  m. 

grains 
per  linear 
inch. 

Per 
cent. 

Diam. 
m.  m. 

grains 
per  linear 
inch. 

Per 

cent. 

Diam. 
m.  m. 

grains 
per  linear 
inch. 

Per 

cent. 

Ito3 

23.1 

.4 

Ito3 

23.1? 

Ito3 

23.1 

.8 

.5tol 

31.7 

3.0 

.5tol 

31.7) 

.5tol 

31.7 

1.2 

.4 

63.5 

6.9 

.4 

63.5 

.4 

.4 

63.5 

2.0 

.3 

84.7 

8.1 

.3 

84.7 

.6 

.3 

84.7 

1.6 

.16 

163.9 

3.0 

.16 

163.9 

.9 

.16 

163.9 

.9 

.12 

211.9 

1.6 

12 

211.9 

1.7 

.12 

211.9 

.3 

.072 

353.4 

1.2 

.072 

353.4 

2.0 

.072 

358.4 

.2 

.047 

510.1 

3.6 

.047 

540.1 

14.3 

.047 

240.1 

2  5 

.036 

704.3 

6.8 

.036 

704.3 

16.2 

.036 

704.3 

3.7 

.025 

1,020. 

14.6 

025 

1,020. 

20.1 

.025 

1,020. 

5.6 

.015 

1,695. 

14.8 

.015 

1,695. 

5.6 

.015 

1,695. 

10.6 

.808 

3,226. 

30.7 

.008 

3,226. 

33.6 

.008 

3,226. 

24.7 

.0001 

25,000. 

4.6 

.0001 

25,000. 

2  5 

.0001 

25,000. 

48.0 

130.  Number  of  Grains  of  Soil  in  a  Cubic  Inch — If  soil 
grains  were  perfect  spheres  like  shot  and  in  a  given  soil 
they  were  all  of  a  single  size  it  would  be  a  simple  matter  to 


FIG.  34. — Showing  the  effect  of  size  and  arrangement  of  soil  grains  on 
the  pore  space  and  upon  the  movement  of  air  and  water  through  a 
soil. 


110  Physics  of  the  Soil. 

determine  the  number  in  a  cubic  inch.  If  a  soil  were  made 
up  entirely  of  the  largest  size  given  in  the  last  table,  then 
23  would  build  one  edge  of  a  cube  an  inch  on  a  side  and 
the  number  in  a  cubic  inch  arranged  in  the  manner  repre- 
sented in  the  upper  part  of  Fig.  34  would  be 

233  =  23  X  23  X  23  =  12, 167. 

On  the  other  hand,  if  they  were  all  the  size  of  the  smallest 
grain  in  the  table  then  the  number  would  be 

25.0003  =15,625,000,000,000, 

or  enough  to  form  three  and  a  third  continuous  lines  of 
grains  in  contact  from  Boston  to  San  Francisco. 

131.  The  Size  of  Soil  Kernels. — It  must  be  kept  in  mind 
that  while  it  is  true  that  the  heavy  clay  soils  are  made  up 
largely  of  soil  grains  of  the  extremely  small  size  considered 
.in  (130)  these  minute  grains  are  generally  bound  together 
in  groups  or  kernels  of  various  sizes  and  it  is  only  by  long 
boiling  in  water  or  thorough  pestling  that  these  can  be 
broken  down.  The  writer  has  found  that  when  air-dry 
samples  of  the  heaviest  clay  soils  are  thoroughly  pestled  in 
the  dry  condition  it  is  difficult  to  reduce  their  texture  to  a 
finer  degree  than  kernels  averaging  .01  to  .005  m.  m.  in 
diameter  or  such  that  from  2,500  to  5,000  are  required  to 
span  a  linear  inch;  but  even  this  degree  of  closeness  of 
texture  is  too  fine  to  allow  of  proper  drainage  and  soil  ven- 
tilation and  to  permit  roots  to  make  their  way  through  tho 
soil  with  the  freedom  required  for  good  crops. 

132.  Specific  Gravity  of  Soil  Grains. — The  specific  gravity 
of  soil  grains,  or  the  number  of  times  they  are  heavier  than 
an  equal  volume  of  water,  varies  somewhat,  as  does  that  of 
the  minerals  which  compose  them.  As  there  are  not  many 
common  minerals  more  than  three  times  as  heavy  as 
water  and  not  many  lighter  than  2.5  times  as  heavy,  the 
specific  gravity  of  soil  grains  will  lie  between  these  two 
figures  and  it  is  usually  found  to  be  near  2.65. 


Texture  of  Soils. 


Ill 


133.  The  Pore  Space  of  Soils — When  the  weight  of  a  cu- 
bic foot  of  dry  soil  is  known  the  amount  of  pors  space  or 
space  not  occupied  by  the  soil  grains  may  be  computed  from 
the  specific  gravity.  Taking  the  weight  of  a  cubic  foot  of 
water  at  62.42  Ibs.,  a  cubic  foot  of  dry  soil,  if  there  were 
no  open  spaces  in  it,  should  be 

2.65  X  62.42  =  165.4  Ibs. 

With  this  value  and  the  data  given  in  (149)  the  pore  space 
of  those  soils  may  be  calculated.  Thus,  for  the  surface 
foot  we  have 

165.4  —  79 

Pore  space  =  —         =  52.23  per  cent. 

-Lou .  4- 

That  is,  in  this  soil  the  surface  foot  is  more  than  half  open 
space.  The  pore  space  for  the  six  feet  will  be  as  given  be- 
low: 


Weight  of 
soil. 

Pore  space. 

Firstfoot        

Lbs. 
79  0 

Per  cent. 
52  23 

92  62 

44  ('<) 

Third  foot        

104.59 

36  76 

Fourth  foot  

10(5  21 

35  78 

Fifth  foot    

111.06 

32  85 

111  06 

31  85 

Thus  it  is  seen  that  the  unoccupied  space  in  a  soil  varies 
from  more  than  half  to  less  than  one-third  of  its  volume, 
the  finest  grained  soils  having  the  largest  pore  space  and 
the  sandy  soils  and  sands  the  smallest. 

134.  Pore  Space  Between  Spherical  Grains. — It  can  be 
shown  mathematically  that  when  a  space  is  filled  with 
spheres  all  of  one  size  and  these  are  given  the  closest  pos- 
sible packing,  having  the  arrangement  shown  in  the  lower 
part  of  Fig.  34  and  in  Fig.  35,  the  pore  space  must  be 
25.95  per  cent. ;  but  when  the  spheres  are  given  the  closest 
possible  packing  and  the  arrangement  represented  in 


112 


Physics  of  the  Soil. 


the  tipper  part  of  Fig.  34,  then  the  pore  space  must 
be  as  large  as  47.64  per  cent.  In  the  first  case  the  water 
capacity  of  such  a  soil  with  the  pores  entirely  filled  would 


FIG.  35. — Showing  the  closest  packing  of  spherical  soil  grains,  the  ele- 
ment of  volume  and  the  direction  of  lines  Of  flow.  Face  angles  60° 
and  120°.  (After  Slichter.) 

be  3.114  acre-inches  per  acre-foot  and  with  the  second  ar- 
rangement the  maximum  water  capacity  would  be  5.7168 
acre-inches  per  acre-foot. 

Neither  of  these  arrangements  would  be  likely  to  occur 
throughout  a  mass,  and  hence  the  general  tendency  will  be 


Texture  of  Soils. 


113 


to  form  a  pore  space  between  these  two  extremes,  and  Fig. 
37  shows  what  the  observed  pore  space  is  in  soils,  sand, 
crushed  rock  and  crushed  glass.  It  will  be  observed  that 


FIG.  36. — Showing  the  closest  packing  of  spherical  grains,  the  element 
of  volume,  and  the  direction  of  lines  of  flow  when  the  face  angles 
are  90°,  60°  and  120°.  (After  Slichter.) 

the  finest  clay  soils,  and  indeed  the  finest  grained  materials, 
have  the  largest  pore  space.  It  will  also  be  noted  that  the 
largest  observed  pore  space  exceeds  the  largest  theoretical 


114 


Physics  of  the  Soil. 


pore  space  and  that  the  smallest  observed  pore  space  also 
falls  below  the  smallest  theoretical  limit  for  spherical 
grains  of  a  single  size. 


FIG.  37.— Showing  the  observed  pore  space  of  different  kinds  of  soils  and 
sands  and  their  relation  to  the  theoretical  pore  space  of  spheres  of 
a  simple  diameter. 

135.  Amount  of  Pore  Space  Determines  Maximum  Water 
Capacity  of  Soil. — The  amount  of  water  a  soil  may  contain 
when  below  the  level  of  the  ground  water  surface  is  meas- 
ured by  the  pore  space.  So  too  in  the  case  of  heavy  and 
protracted  rains  the  pore  space  determines  the  number  of 
inches  of  water  which  may  enter  the  ground  before  it  be- 
comes so  filled  that  surface  drainage  must  carry  away  that 
which  is  falling,  and  it  will  be  readily  understood  that  in 
the  clay  soils,  where  the  pore  space  is  so  high,  very  large 


Texture  of  Soils.  115 

amounts  of  water  may  be  stored  in  them  to  drain  away 
gradually  in  the  underflow. 

136.  Subdivision  of  Fore  Space  Determines  the  Rate  of  Per- 
colation and  Drainage. — If  reference  is  again  made  to  Fig. 
34  it  will  be  clear  at  a  glance  that  Avater  must  flow  through 
spaces  filled  with  these  different  sizes  of  spheres  at  very 
different  rates.     Where  the   spheres  are  largest  there  are 
16  passage-ways  for  the  movement  of  air  or  of  water ;  but  in 
the  middle  section  where  the  spheres  have  one-half  the 
diameter,  the  number  of  passages  is  4  times  as  great,  while 
in  the  last  section  with  spheres  of  one-quarter  the  size  the 
number  of  passages  is  16  times  as  great. 

The  aggregate  area  of  the  cross-sections  of  the  pores  is 
exactly  the  same  in  the  three  cases,  and  from  this  it  follows 
that  the  areas  of  the  cross-sections  of  single  pores  are  to 
each  other  as  16  :  4  :  1. 

The  coarse  spheres  divide  the  column  of  water  into  16 
streams,  the  medium  ones  divide  it  into  64  streams,  while 
the  smallest  spheres  divide  the  column  into  256  streams, 
each  having  only  one-sixteenth  the  sectional  area  of  the 
first.  But  to  subdivide  the  column  into  256  streams  in- 
stead of  16  means  that  the  friction  must  be  much  greater 
in  the  aggregate  on  the  smaller  streams,  and  hence  that  the 
flow  must  be  slower. 

137.  Method  of  Determining  the  Pore  Space  of  Soil — The 
simplest  method  of  determining  the  pore  space  of  soil  is  to 
pack  the  dry  material  into  a  cylindrical  vessel  containing 
100  c.  c.  until  it  is  even  full,  and  then  weigh  and  compute 
the  per  cent,  of  pore  space  from  the  volume,  weight  and 
specific  gravity,  using  the  formula 

Vd  — W  _  p 


Vd 


where  V  is  the  volume  of  the  vessel  in  c.  c.,  d  is  the  specific 
gravity  and  W  is  the  weight  of  the  soil  in  grams. 

To  determine  the  pore  space  in  undisturbed  field  soil 


116  Physics  of  the  Soil. 

the  simplest  method  is  to  use  a  soil  tube,  represented  in 
Fig.  38,  taking  a  number  of  cores  of  the  desired  depth, 


FIG.  38.— Showing  soil  tube  for  taking  samples  of  soil. 

drying  them,  and  then  compute  the  pore  space  with  the 
formula  above. 

138.  Largest  Possible  Pore  Space.— The  largest  possible 
pore  space  in  soils  will  be  found  in  the  cases  where  the  com- 
pound or  kernel-structure  is  most  marked.  Referring 
again  to  Fig.  34,  imagine  each  sphere  there  represented 
to  be  made  up  of  other  very  much  smaller  spheres  having 
the  same  general  arrangement.  Were  this  the  cass  it  is 
clear  that  in  consequence  of  the  compound  spheres  the  soil 
must  have  a  pore  space  not  less  than  25.95  per  cent,  with 
one  arrangement  and  47.64  per  cent,  with  the  other.  But 
in  addition  to  this  pore  space  there  must  be  a  like  pore 
space  within  each  compound  sphere  so  that  in  the  first  case 
the  total  pore  space  would  be 

25.95  -f  [25.95  per  cent,  of  (100  —  25.95)]  =  45.17 
and  in  the  second  case 

47.64  4-  [47.64  per  cent,  of  (100  —  47.64)]  =  72  58  per  cent. 

The  first  pore  space,  45.17,  it  will  be  seen,  lies  close 
to  that  possessed  by  the  finer  soils  but  the  latter  is  larger 
r.han  anything  ever  found  except  it  be  in  the  loose  mulches. 

The  smallest  pore  spaces  result  when  grains  of  different 
sizes  are  so  related  that  the  small  ones  fall  into  the  pores 
formed  by  the  large  ones  without  at  the  same  time  crowd- 
ing them  farther  apart.  Referring  again  to  Fig.  34,  it 
will  be  seen  that  if  small  spheres  are  packed  into  the  pores 
there  shown,  with  the  same  arrangement  that  the  large 
ones  have,  the  original  25.95  per  cent,  and  47.64  per  cent. 


Texture  of  Soils. 


117 


of  pore  space  would  be  occupied  to  the  extent  of  74.05 
per  cent,  in  the  first  case  and  of  52.36  per  cent,  in  the 
second  case.  Such  a  condition  would  leave  only  about 
6.73  per  cent,  of  pore  space  for  the  closest  packing. 

Such  arrangements  as  this  are  not  likely  of  course  to 
occur  in  nature  but  in  the  construction  of  macadam  roads 
and  in  all  concrete  work  a  definite  effort  is  made  to  reduce 
the  pore  space  to  the  smallest  possible  limit  by  using 
crushed  rock,  gravel,  sand  and  finally  cement  to  fill  all 
pores  as  completely  as  possible. 

139.  Number  of  Soil  Grains  per  Unit  Weight.  —  If  soil 
grains  were  all  spheres  and  in  a  given  case  they  were  all 
of  the  same  size  the  number  in  a  gram  could  be  found  by 
the  equation 

Weight  of  soil 
No.  of  grams  = 


where  the  weight  of  the  soil  is  in  grams  and  the  diameter 
of  the  soil  grains,  d,  is  in  c.  m. 

In  the  table  below  are  given  in  round  numbers  the  num- 
ber of  grains  in  one  gram  and  in  one  pound  of  soil,  sup- 
posing the  grains  all  spheres  and  to  have  a  specific  gravity 
of  2.65. 


Diameter. 

No.  of  grains  in 
one  gram. 

No.  of  grains  in  one  Ib. 

720 

396  90S 

720,000 

3°6  90M  000 

720,000,000 

396  ^03  000  OUO 

001  m  m            

720,000  OOo  000 

3?6  90.1  000  000  000 

.  0001  m.  m.  ... 

720,  OU),000,  000,  OUO 

396  903  000  OOO'  000,000 

That  is  to  say,  720  multiplied  by  10  used  as  a  factor  3, 
6,  9  and  12  times  gives  the  number  of  grains  in  a  gram 
of  soil  in  round  numbers  and  the  number  in  a  pound  may 
be  found  by  using  10  as  a  factor  in  the  same  way  and 
the  number  326,903. 

If  the  soil  were  made  up  of  some  grains  of  all  the  sizes 


118 


Physics  of  the  Soil. 


in  the  table,  then  to  find  the  total  number  in  a  gram  or 
pound  it  would  be  necessary  to  multiply  those  numbers 
by  the  per  cent,  of  each  size  found  in  a  gram  of  the  soil 
and  add  the  several  products.  If  the  soil  were  made  up 
of  20  per  cent,  of  each  size  in  the  table  the  number  would 
be  as  follows: 


Diameter. 

Per  cent. 

No.  of  grains  per  gram. 

20 

144 

20 

141  0  0 

20 

1-14,  OMI.  (MO 

001  m.  m    

20 

144,0>«>,t<X)  100 

20 

144  000  (OJ  000  CUO 

Total    

144,144  144  144  144 

140.  Amount  cf  boil  Surface  Possessed  by  a  Gram  of  Soil. 
— Much  of  the  water  retained  by  soils  is  held  there  in  the 
form  of  thin  films  surrounding  the  grains  and  the  larger 
this  surface  is  the  more  water  may  be  retained.  So,  too, 
the  solution  of  plant  food  from  the  grains  takes  place  at 
their  surfaces  and  the  larger  the  amount  of  surface  the 
more  rapidly  the  solution  may  take  place. 

The  extent  of  soil-surface  in  a  gram  of  soil  can  be  found 
by  multiplying  the  number  of  grains  by  the  surface  of  one 
grain  or  by  introducing  ird2  into  the  equation  of  (139), 
thus: 

Weight  X  *d*        6  X  weight 

— is*        =  T-9 —      —  =  s011  surface 

ffd3  X  sp-  gr«        d  X  sp-  gr. 

6 
expressed  in  square  c.  m. 

Using  this  formula  to  compute  the  surface  in  one  gram 
of  soil  grains  having  the  sizes  given  in  the  table  of  (139) 
the  results  below  are  obtained: 


Surface  per  gram  Surface  per  pound 


Diameter  in  grains. 

sq.  cm. 

sq.  feet. 

1.  m.  m  

22  64 

11  05 

.1  m.  m  

226  41 

110  54 

.01  m.  m....  

2,264  15 

1  105  38 

.001  m.  m  

22,641  51 

11,053  81 

.0001  m.  m  

2"o,415  14 

110  538  16 

Internal  Surface  of  Soils.  119 

It  will  he  seen  from  this  table  that  the  internal  surface 
of  an  ideal  soil  increases  in  the  same  ratio  that  the  diam- 
eter of  the  grains  decreases,  that  is,  reducing  the  diameter 
one-half  doubles  the  surface  to  which  water  may  adhere 
and  upon  which  it  may  act 

141.  Difficulties  in  Determining  the  Surface  of  a  Soil  Accu- 
rately.— While  it  is  possible  to  determine  accurately  the 
surface  in  a  given  weight  of  spheres  of  known  dimensions 
the  case  is  quite  different  with  true  soils.  Indeed,  it  is 
not  practicable  to  determine  Tvith  much  accuracy  the  sur- 
face in  a  soil.  This  will  be  clear  from  a  consideration 
of  a  simple  problem. 

Take  a  soil  composed  of  grains,  (a)  .009  and  (b)  .00015 
m.  m.  in  diameter  and  let  these  be  mixed  in  the  propor- 
tions of 

A.  90  per  cent,  of  (a)  with  10  per  cent,  of  (b). 

B.  10  per  cent,  of  (a)  with  90  per  cent,  of  (b). 

C.  50  per  cent,  of  (a)  with  50  per  cent,  of  (b). 

Under  these  conditions  the  surface  of  one  gram  of  such 
mixtures  of  soil  having  a  specific  gravity  of  2.65  is 

For  A. 

Surface. 

80  per  cent,  of  grains  fa)  .009  m.  m.  diameter 2,26isq.cra. 

10  per  cent,  of  grains  (b)  .00015  m.  m.  diameter 15,  OJi  sq.  cm. 

Totalsurface - 17,358  sq.  cm. 


ForB. 

10  per  cent,  of  grains  (a)  .009  m.  m.  diameter 251. 6  sq.  cm. 

90  per  cent,  of  grains  (b)  .00015  m.  m.  diameter 135, 848.9  sq.  cm. 

Totalsurface 136, 100. 5  sq.  cm. 


ForC. 

60  per  cent,  of  grains  (a)  .009  m.  m.  diameter 1,258.0  sq.  cm. 

50  per  cent,  of  grains  (b)  .00015  m.  m.  diameter 75,481.7  sq.  cm. 

Total  surface 70,739  7  sq.  cm. 


120 


Physics  of  the  Soil. 


The  number  of  grains  in  one  gram  of  each  of  these  mix- 
tures would  be  as  given  below : 


A. 

R 

C. 

(a)  .. 

889,753,061 

98,861,363 

494,306,8!8 

(b)  

21,354,187,192,118 

192,188,053,097,315 

106,  770,  833,  333,  333 

Total  

2J,35%076>945,lli9 

192,188,151,958,708 

106,771,327,610,151 

It  is  the  custom  to  find  the  diameter  of  soil  grains 
cither  by  direct  measurement  or  else  by  counting  and 
weighing  a  given  number  of  grains  and  then  computing  the 
diameter  of  the  mean  grain  from  the  weight  and  specific 
gravity.  If  the  diameter  of  the  mean  grain  in  the  above 
three  problems  is  computed  by  each  of  these  methods  the 
results  will  be  as  below: 

If  the  surface  of  a  gram  of  soil  is  computed  from  each 
of  these  diameters  the  results  given  below  will  be  found : 


A. 

B. 

•    c. 

Actual  surface  per  gram  of  soil  

sq.  cm. 
17,358 

sq.  cm. 
136,101 

sq.  cm. 
76,740 

Surface  computed  from  the  grain  of  mean  diameter 
Surface  computed  from  the  grain  of  mean  weight.. 

150,  570 
10,053 

150,9.i9 
145,734 

150,902 
119,804 

These  results  are  very  different  and  differ  so  much  from 
the  actual  as  to  make  them  of  little  value  in  determining 
the  actual  surface  a  given  soil  may  possess. 

It  has  been  the  practice  to  take  as  the  mean  diameter 
of  the  soil  grain  the  average  between  the  diameter  of  the 
largest  grain  in  the  group  and  the  smallest,  which  in  the 
above  problem  wrould  give  .004575  as  the  mean  value. 

But  to  use  this  to  compute  the  surface  in  a  gram  of  soil 
would  give  the  results  below : 


Computed  from 
the  mean  of  the  two 
eAireine  diameters. 

A. 

B. 

C. 

4,949  sq.  cm. 

17,358sq.  cm. 

138,101  sq.  cm. 

7G,"40sq.  cm. 

Internal  Surface  of  Soils.  121 

Here  it  is  seen  that  the  computed  surface,  4,949,  is  very 
far  indeed  from  either  of  the  true  values  given  under  A, 
B  and  C. 


142.  Effective  Diameter  of  Soil  Grains. — While  it  is  not 
possible  to    determine    either  the  mean    diameter  of  the 
grains  in  an  ordinary  soil  or  the  amount  of  surface  a  given 
weight  of  soil  may  possess  with  even  approximate  accu- 
racy, it  is  possible  for  the  simple  sands,  at  least,  to  deter- 
mine the  diameter  of  a  grain  which,  if  substituted  for  the 
actual  ones,  would  permit,  under  like  conditions,  the  same 
amount  of  air  or  of  water  to  flow  through. 

The  method  is  based  upon  the  laws  of  flow  of  fluids 
through  capillary  tubes  and  aims  to  compute  from  the  ob- 
served rate  of  flow  of  air  through  a  given  column  of  soil 
the  effective  diameter  of  the  capillary  pores  and  from  this 
the  size  of  spherical  grains  which  would  be  required  to 
form  such  capillary  tubes  as  those  computed.  The  theory 
of  the  method  is  fully  set  forth  in  Prof.  C.  S.  Slichter's 
paper.1 

143.  Description  of  the  Method. — The  apparatus  used  to 
determine  the  effective  size  of  soil  grains  is  represented  in 
Fig.   39,  and  consists  of  a  cylinder  in  which  a  sample 
of  soil   is   carefully  packed   and  weighed   to   determine 
the  per  cent,  of  pore  space.     When  this  has  been  done 
the  tube  is  connected  with  the  aspirator  and  the  rate  at 
which  air  will  flow  through  it  under  a  measured  tempera- 
ture and  pressure  found.     When  these  data  have  been  ob- 
tained, then  the  formula  below,  used  with  the  table  given, 
enables  the  effective  diameter  to  be  computed  when  the 
flow  has  been  measured  at  the  temperature  of  20°  C. 


1  Nineteenth  Annual  Report  of  the  U.  S.  Geol.  Survey,  Part  II. 


122 


Physics  of  the  Soil. 


spt 


[8.9434  — 10] 


where 

d  =  diameter  of  grain  in  c.  m. 

h  =  length  of  sand  column  in  c.  m. 

8  =  area  of  cross-section  of  sand  column  in  sq.  c.  m. 

p  =  pressure  in  c.  m.  of  water  at  20°  C. 

t  =  time  in  sec.  for  5,000  c.  c.  of  air  to  flow  through  at  a  torn 

perature  of  20°  C. 

[8.9434  —  10]  is  a  logarithm  of  a  constant 
k  is  a  constant  taken  from  the  following  table. 


FIG.  39. — Showing  aspirator  for  determining  the  mean  effective  diameter 
of  soil   grains.    A,    aspirator  bell;    B,   pressure  gauge;   C,   air   meter; 
D,  aspirator  tube  for  samples. 


Movements  of  Fluids  Through  Soils.  123 


Per  cent,  of  pore 

space. 

Log.  k. 

d. 

Per  cent,  of  pore 
space. 

Log.  k. 

d. 

26 

1  9°58 

563 

37... 

4193 

377 

27  

1.8695 

500 

38  

.3816 

«71 

28    

1  8195 

490 

39  

3445 

367 

29  

1.7701 

502 

40  

.3u.~8 

353 

•JO  

.7199 

467 

41  

2725 

351 

31  

.67*2 

455 

42  

1.2374 

345 

32  

.6277 

430 

43  

1.2024 

339 

33    

.5*47 

438 

n  

1  1690 

320 

34        

5109 

410 

45  

1  1370 

312 

35  

.4999 

407 

46... 

1  1058 

329 

S6  

.4592 

400 

47  

1  0729 

144.  Observed  Flow  of  Water  Through  Sand  Compared 
With  That  Computed  From  the  Effective  Diameter. — The  ac- 
curacy of  the  method  described  in  (143)  is  best  shown  by 
computing  from  the  effective  diameter  of  the  soil  grains 
what  the  flow  of  water  ought  to  be  and  then  measuring  the 
flow  of  water  to  see  how  it  corresponds.  This  has  been 
done  and  the  results  are  given  in  the  table  below : 


Grade  of  sand. 

Effective 
diameter  of 
grain. 

Computed 
flow  of  water. 

Observed 
flow  of  water 

8... 

m.  m. 
2.54 

Gms. 
2,277 

Gms. 
2,296 

7 

1  808 

1,132 

1,080 

6  

1.451 

757 

756 

f,H  

1.217 

522 

542 

5  

1.095 

453  2 

504  6 

4  

.9149 

297.5 

3^9.2 

3  

.7988 

193 

210  0 

2  

.7146 

122 

138  6 

1  

.6006 

80.6 

94.8 

0  

.5169 

66.8 

T2.3 

When  it  is  observed  that  the  effective  diameter  of  the 
grains  in  these  sands  was  found  by  measuring  the  flow  of 
air  through  one  sample  in  one  piece  of  apparatus  and  the 
flow  of  water  was  measured  through  another  sample  and 
in  another  piece  of  apparatus-,  and  that  the  flow  varies  as 
the  squares  of  the  diameters  of  the  soil  grains,  it  is  clear 
that  the  effective  diameter  has  a  very  exact  value  so  far  as 
the  flow  of  fluids  is  concerned. 


124 


Physics  of  the  Soil. 


145.  The   Effective   Diameters   of   Soil    Grains   and   the 

Amount  of  Surface   Computed  From  Them We  have  no 

means  of  knowing  yet  how  accurately  the  computed  sur- 
face of  soil  grains  in  a  given  weight  of  sample  compares 
with  that  which  is  possessed  by  it.  We  do  know,  however, 
that  the  comparison  is  accurate  enough  to  furnish  a  valua- 
ble basis  for  comparing  different  types  of  soils,  and  in  the 
table  which  follows  is  given  the  effective  diameters  of  sev- 
eral kinds  of  soils,  together  with  the  pore  space  and  the 
computed  amount  of  soil  surface  per  cubic  foot  of  dry  soil. 

Table  of  computed  surface  of  soil  grains  in  different  types 

of  soil. 


Kind  of  soil. 

Effective 
diameter  of 
soil  grains. 

Per  cent. 
of 
pore  space. 

Surface  of  soil 
grains  in 
one  cubic  foot. 

Finest  clay  soil  

m.  m. 
.004956 

52  94 

Sq.  Ft. 
173  700 

Fine  clay  soil  

.007657 

45  69 

129  100 

Fine  clay  soil  

.008612 

48  00 

110,  500 

Heavy  red  clay  soil  

.01111 

44  15 

91  960 

Loamy  clay  soil  

.02542 

49  19 

70  500 

Clayey  loam  

01810 

47  10 

53  490 

Loam  

02197 

44  15 

46  510 

.02619 

34  49 

45  760 

.03035 

38  83 

36,880 

Sandy  soil  

.07555 

34  45 

15  870 

Sandy  soil  

.1119 

32  49 

11  030 

Coarse  sandy  soil  

1432 

34  91 

8  818 

It  will  be  seen  from  this  table  that  the  amount  of  surface 
in  the  true  soils  is  indeed  very  great,  ranging  from  a  little 
less  than  a  quarter  to  more  than  a  third  of  an  acre  in  the 
sandy  soils,  through  more  than  an  acre  in  the  loams  to  as 
much  as  four  acres  per  cubic  foot  in  the  finest  clay  soils. 
The  amount  of  soil  surface  in  the  upper  four  feet  of  every 
cultivated  field  ranges  from  not  less  than  one  acre  to  more 
than  16  acres  per  each  square  foot  of  surface  cultivated. 

146.  Relation  of  the  Surface  of  Soil  Grains  to  the  Water 
Capacity — A  large  portion  of  the  water  held  by  a  soil  is 
spread  out  as  a  thin  film  surrounding  the  soil  grains  and  it 


Movements  of  Fluids  Through  Soils.  125 

is  generally  true  that  the  larger  the  surface  of  the  soil 
grains  the  more  water  the  soil  will  retain. 

If  a  marble  is  lifted  out  of  water  it  retains  a  film  sur- 
rounding it  and  its  surface  is  wet;  so  if  rains  fall  upon  a 
sand  or  soil  surface  until  percolation  takes  place,  there  is 
held  back  upon  the  grains  a  certain  amount  of  water  which 
is  characteristic  of  or  peculiar  to  each  type.  It  is  clear 
that  a  soil  whose  internal  surface  is  4  acres  per  cubic  foot 
may  contain  a  large  amount  of  water  even  though  the  film 
is  extremely  thin.  In  an  acre  there  are  43,560  sq.  ft.  and 
in  four  acres  174,240  sq.  ft.  The  thickness  of  a  water 
film  on  this  surface  sufficient  to  equal  4  inches  on  the  level 
per  square  foot  of  soil  would  be 

17172*0  =  13^60  ofaninch 

or  one-half  the  thickness  of  the  film  of  a  soap  bubble  when 
it  becomes  yellow  just  before  appearing  black  and  breaking, 
from  thinning  out.  This  thickness  is  also  about  -J  the  di- 
ameter of  the  soil  grain  itself. 

In  the  case  of  a  fine  sand  having  grains  .08188  m.  m., 
which  retains,  after  complete  drainage  8  feet  above  stand- 
ing water,  3.44  per  cent,  of  water,  the  film  would  have  to 
have  a  thickness  of  only  about  *Y  of  the  diameter  of  the 
grain,  and  when  containing  20  per  cent,  of  its  dry  weight 
then  the  film  need  have  a  thickness  of  only  about  &  of  the 
diameter  of  the  sand  grains,  that  is,  .0072  m.  m. 

It  is  clear,  therefore,  from  these  considerations  that  the 
surface  of  soil  grains  has  much  to  do  in  determining  the 
water-holding  power  of  a  soil  and  that  the  films  may  be 
very  thin  and  yet  on  account  of  their  great  extent  represent 
a  high  per  cent,  of  the  soil  itself. 

147.  Movement  of  Air  Through  Soil. — There  is  perhaps 
nothing  which  shows  how  physically  different  the  fine  and 
the  coarse  grained  soils  are  as  clearly  as  the  rates  at  which 
air  will  pass  through  them  when  dry,  and  in  the  next  table 
some  of  these  are  given. 


126 


Physics  of  the  Soil. 


It  will  be  seen  from  this  table  that  when  the  grains  are 
so  large  that  10  of  them  will  span  a  linear  inch  only  37 
seconds  are  required  for  a  pressure  of  .1  foot  of  water  to 
force  5,000  c.  c.,  5.3  quarts,  of  air  through  a  column  a  foot 
long  and  .01  of  a  square  foot  in  cross  section ;  but  in  the 
finest  clay  soil,  which  makes  the  best  grass  land,  where 
5,125  grains  must  be  set  in  line  to  measure  a  linear  inch, 
then  the  time  required  is  2,933,000  seconds  for  the  same 
amount  of  air  under  the  same  conditions  to  be  forced 
through,  a  ratio  of  37  seconds  to  nearly  34  days. 

Table  showing  the  differences  in  the  rate  of  movement  of  air 
through  gravel,  sand  and  soils  of  different  types  when  the 
columns  are  1  foot  long,  .01  ft.  in  cross  section  and  under  a 
pressure  of  .1  ft.  of  water. 


Description  of  material. 

No.  of  grains 
per 
linear  inch. 

Per  cent. 
of 
pore  space. 

No.  of  seconds 
for  5,000  c.  c. 
of  air  to  tiow 
through. 

10. 

37  60 

37 

14.0 

38.44 

67 

17.5 

38.85 

99 

20  6 

39.26 

138 

24.3 

39.88 

184 

27.8 

38.53 

260 

31.8 

36.26 

418 

35.5 

34.66 

6)2 

Medium  saiid,  grade  No.  1  

42.3 

34.43 

869 

49  1 

34.42 

1,178 

Fine  sand,  grade  No  60  

143 

34.20 

10,370 

Fine  sand,  grade  No.  100  

310 

35.32 

44,310 

177 

34.91 

14,580 

227 

32.49 

30,460 

336 

34.45 

54,910 

837 

38.83 

227,  400 

970 

34.49 

45,750 

1,156 

44.15 

2^2,200 

1,403 

47  10 

476,600 

1,647 

40.19 

804,600 

2,286.0 

44.15 

1,129,000 

2,949.0 

48.00 

1,412,000 

3,  310.0 

45  96 

2,057,000 

5,125.0 

52.94 

2,933,000 

It  should  be  understood  that  this  slow  rate  of  movement 
of  air  through  the  finest  clay  soils  was  observed  when  the 
air-dry  soil  had  been  pulverized  in  a  mortar  and  made  as 
fine  as  practicable  before  packing  into  the  aspirator.  Un- 


Movements  of  Fluids  Through  Soils.  127 


der  field  conditions,  as  has  been  pointed  out,  a  good  clay 
soil  has  its  clusters  of  various  sizes  and  there  are  passage- 
ways of  various  sizes  and  forms  which  allow  both  air  and 
water  to  move  much  more  freely  than  has  been  recorded 
in  the  table  and  if  it  were  not  so  plants  could  not  thrive 
in  them. 

148.  Permeability  to  Air  of  Undisturbed  Field  Soils. — The 
rate    at    which    air    may    flow 

through  soils  in  their  natural 
condition,  in  place  In  the  field, 
may  be  readily  studied  with  an 
apparatus  such  as  is  shown  in 
Fig.  40.  When  the  soil  tube 
A  is  driven  into  the  ground  to 
near  the  depth  at  which  the 
flow  of  air  is  to  be  measured  it 
is  recovered,  the  core  of  soil  re- 
moved and  the  tube  returned  to 
its  place,  when  the  aspirator  is 
connected  as  shown  in  the  cut, 
and  the  time  required  for  a 
given  volume  of  air  to  be  drawnFiG.  40- showing  apparatus  for 

MirrmrrVi  r\r>tf>rrr\\nf*r\  Tn  tlipcp  measuring  the  permeability  to 
nilOllgn  C  .Q.  in  tnese  ajrof  soils  in  the  field.  A  core  of 

field     Studies     it    will    be    found        soil    is   removed   to   the  (le.-ired 

depth  and  the  soil  tube  replaced. 

that  the  dryer  the  soils  are  the 

more  freely  air  passes  through  them  but  that  when  they 
are  saturated  with  water,  as  just  after  heavy  rains,  little 
or  no  air  will  pass  through  them  even  under  a  pressure  of 
12  inches  of  water. 

149.  Weight  of  a  Cubic  Foot  of  Dry  Soil. — A  cubic  foot  of 
undisturbed  air-dry  soil  varies  in  weight  between  quite 
wide  limits,  the  humus  soils  being  the  lightest,  and  the 
coarse  sandy  soils  the  heaviest.    The  writer  has  found  a  dry 
soil  to  have  the  weight  per  cubic  foot  given  in  the  table  be- 
low: 


128 


Physics  of  the  Soil. 


1st  foot. 

2d  foot. 

3d  foot. 

4th  foot. 

5th  foot. 

6th  foot. 

Pounds  per  cubic  foot 
Pounds  per  acre  

79 
2,740,000 

92.6;; 

4,034,000 

104.59 
4,557,000 

106.21 
4,637,000 

111.06 

4,840,000 

111.06 

4,840,000 

Shubler  gives  the  weight  of  a  cubic  foot  of  dry  soil  as 
follows : 

Dry  calareous  or  siliceous  sand 110  Ibs. 

Half  sand  and  half  clay 96  Ibg. 

Common  arable  soil 80  to  90  Ibg. 

Heavy  clay 75  Ibs. 

Garden  mould  rich  in  vegetable  matter 70  Ibs. 

Peat  soil 30  to  50  Ibs. 

As  a  number  easy  to  remember  it  may  be  taken  as  a 
safe  figure  that  the  mean  weight  of  the  surface  four  feet 
of  field  soils  is,  in  round  numbers,  4,000,000  Ibs.  per  acre- 
foot. 

150.  Heavy  and  Light  Soils. — These  terms  are  used  more 
with  reference  to  the  ease  with  which  soils  may  be  worked 
than  to  their  weight  per  cubic  foot.  A  soil  that  is  nat- 
urally mellow  and  easily  stirred  is  called  a  light  soil, 
while  one  that  becomes  hard  when  dry  and  which  tends  to 
form  clods  is  often  called  heavy.  Sandy  soils,  as  shown  in 
(149)  are  among  the  heaviest  we  have  while  the  clayey  va- 
rieties are  the  lightest  by  weight  except  the  humus  types. 
The  prairie  loams  which  contain  much  humus  and  the 
black  swamp  soils  when  drained  are  among  the  most  mellow 
of  all  soils,  the  large  amount  of  humus  preventing  the  soil 
grains  from  adhering  and  baking. 


CHAPTEK  V. 
SOIL   MOISTURE. 

151.  Occurrence  of  Moisture  in  the  Soil. — For  purposes  of 
discussing  the  cultural  relations  of  soil  moisture  water  may 
be  said  to  occur  in  the  soil  under  three  conditions : 

(1)  That  which  fills  the  pore  spaces  between  the  soil 
grains  and  is  free  to  move  under  gravitational  or  hydro- 
static pressure  and  may  be  called  gravitational  or  hydro- 
static water. 

(2)  That  which  adheres  to  the  surfaces  of  soil  grains 
and  to  the  roots  of  plants  in  films  thick  enough  to  allow 
surface  tension  to  move  it  slowly  from  place  to  place,  and 
which  may  be  called  capillary  water. 

(3)  That  still  retained    on  the  surfaces  of  soil    grains 
when  they  become    air-dry;  whose    chief  movements    are 
those  of  evaporation  and  condensation  and  which  has  been 
designated  hygroscopic  moisture. 

152.  Gravitational  Water. — When  water  in  a  soil  in- 
.creases  in  quantity  sufficiently  to  move  readily  under  the 
pull  of  gravity  it  may  be  harmful  in  three  ways:      (1)  by 
washing  out  the  soluble  plant  foods,  thus  leaving  the  soil 
poor ;  (2)  by  excluding  the  air  and  thus  causing  suffocation 
of  the  roots  of  plants  and  micro-organisms  living  in  the 
soil;  (3)  by  preventing  surface  tension  and  by  dissolving 
cementing  materials,  thus  destroying  or  reducing  the  gran- 
ulation of  soils,  injuring  their  texture.     It  may  be  helpful 
in  two  ways :      ( 1 )  by  replenishing  the  capillary  moisture 
when  this  has  become  too  small  to  enable  crops  to  supply 
themselves,  and  (2)  by  washing  out  and  carrying  away  sol- 
uble substances  wyliich,  if  allowed  to  accumulate,  become  in- 


130  Physics  of  the  Soil. 

jurious,  such  as  black  alkalies  and  possibly  toxic  principles 
developed  by  the  roots  of  plants  or  soil  organisms  or  during 
their  decay. 

153.  Capillary  Water. — It  is  in  this  condition  or  quantity 
in  the  soil  from  which  crops  and  soil  organisms  chiefly  de- 
rive their  supply  of  water,  and  the  right  amount  at  all 
times  is  therefore  very  important.     It  is  in  the  capillary 
water,  too,  that  most  of  the  plant  foods  derived  from  the 
soil  are  held  in  solution  and  with  it  moved  to  the  plants  as 
needed.     When  the  texture  of  the  soil  is  right  the  capillary 
water  simply  surrounds  the  soil  grains  and  soil  granules 
as  a  thin  sheet  which  is  continuous  where  the  grains  are 
nearly  or  quite  in  contact,  but  there  are  always  open  spaces 
through  which  the  air  may  circulate  and  supply  the  needs 
of  roots  and  soil  bacteria. 

If  the  soil  is  puddled  and  the  granules  broken  down  then 
the  surface  films  on  the  smaller  soil  grains  come  so  nearly 
in  complete  contact  that  there  is  insufficient  room  for  air 
to  diffuse  and  plants  cannot  thrive  in  it. 

154.  Hygroscopic  Water — Moisture  in  this  form  possibly 
plays  an  important  part  in  the  actual  solution  of  plant  food 
from  the  soil  and  fertilizer  grains  because  it  is  this  portion 
which  lies  in  immediate  contact  where  the  action  must  take 
place;  but  if  this  is  true  it  can  only  do  its  work  rapidly 
when  capillary  water  is  also  present  to  carry  away  from 
the    dissolving   surfaces   the    products    which    are    being 
formed. 

Polished  surfaces  do  not  as  readily  rust  as  those  which 
have  become  tarnished  or  otherwise  roughened.  When  a 
steel  knife  blade  has  become  a  little  rusty  the  rusting  then 
goes  on  much  more  rapidly,  possibly  because  each  particle 
of  rust  becomes  invested  with  its  film  of  hygroscopic  mois- 
ture, and  when  these  lie  against  the  fresh  metal  the  water 
can  have  a  greater  thickness  and  permit  a  more  rapid  move- 
ment of  the  compounds  formed,  away  from  the  corroding 
surface. 


Water  Capacity  of  Soils. 


131 


It  is  not  probable,  however,  that  the  hygroscopic  mois- 
ture of  a  soil  can  in  any  direct  way  aid  plant  growth. 

155.  Ways  of  Expressing  the  Water  Content  of  Soils. — The 
amount  of  water  a  soil  will  or  may  contain  has  been  ex- 
pressed in  different  ways:  (1)  As  a  per  cent,  of  the  wet 
weight  of  the  soil,  (2)  as  a  per  cent,  of  the  dry  weight  of 
the  soil,  (3)  as  a  per  cent,  of  the  volume  of  the  soil,  (4) 
in  pounds  per  cubic  foot,  (5)  in  inches  per  cubic  foot.  The 
amount  of  moisture  a  soil  does  contain  may  be  most  readily 
and  precisely  stated  as  per  cents,  of  the  wet  or  dry  weight, 
but  for  agricultural  purposes  it  is  best  to  state  the  amount 
in  per  cent,  of  the  volume  or  in  inches  per  cubic  foot. 

156.  The  Maximum  Water  Capacity  of  Soils. — The  largest 
amount  of  water  a  soil  may  contain  is  expressed  by  its  per 
cent,  of  pore  space  and  if  reference  is  made  to  the  table  in 
( 145)  it  will  be  seen  that  this  ranges  from  about  32  to  more 
than  52  per  cent,  that  is  from  4  to  6  acre-inches  per  acre- 
foot  of  soil,  and  from  20  to  32  Ibs.  per  cubic  foot.     These 
amounts  of  water,  however,  are  never  found  in  soils  under 
field  conditions. 

157.  Water  Capacity  of  Soils  Under  Field  Conditions 

The  amount  of  water  which  may  be  retained  by  soils  under 
field  conditions  is  extremely  variable  and  depends  upon  a 
number  of  factors.     In  the  table  below   are  given   the 
amounts  of  water  which  were  found  in  three  types  of  soil 
with  the  undisturbed  field  texture,  when  they  contained  as 
much  as  they  would  retain  after  a  few  days  of  drainage  fol- 
lowing heavy  rains. 

Capacity  of  field  soils  for  moisture. 


Depth. 

Sandy  loam. 

Clay  loam. 

Humus  soil. 

First  foot  

Per  cent. 
17  65 

Per  cent. 
22.67 

Per  cent. 
44  72 

14  59 

19  78 

31  24 

Third  foot      

10  67 

18  16 

21  29 

132 


Physics  of  the  Soil. 


In  this  table  the  third  foot  in  each  case  is  more  or  less 
sandy  and  for  this  reason  shows  percentagely  less  water 
than  the  soil  above.  It  will  be  seen  that  the  surface  foot 
of  sandy  loam  contains  the  smallest  per  cent,  of  water  and 
the  humus  soil  the  largest,  but  on  account  of  the  differences 
in  dry  weight  of  these  soils  their  water  contents  are  more 
nearly  equal  than  they  appear,  the  sandy  loam  containing 
about  16  Ibs.,  the  clay  loam  18  Ibs.  and  the  humus  soil 
26  Ibs.  per  cubic  foot.  Expressed  in  inches  the  amounts 
stand  3,  3.5  and  5  inches  nearly. 

158.  Maximum  Capacity  of  Undisturbed  Field  Soil. — In 
the  table  below  are  given  the  amounts  of  water  which  com- 
pletely filled  the  first  five  feet  of  undisturbed  field  soil^  as 
determined  by  driving  6-inch  metal  cylinders  one  foot  long 
into  the  soil  and,  recovering  them,  covering  the  bottoms 
with  perforated  covers  and  then  placing  the  cylinders  un- 
der water  until  the  pores  became  completely  filled. 

Table  showing    maximum  capacity  of  undisturbed  field  soil 

for  water. 


Kind  of  soil. 

Depth. 

Per  cent. 
of  water. 

Inches  of 
water. 

1st  foot  

41.3 

5  88 

2d  foot  

28  1 

5.03 

3d  foot  

28.4 

5.07 

Clay  with  sand  

4th  foot  
5th  foot  

24.8 
17.4 

4.67 
3.76 

Total               

24.41 

In  this  case  it  is  seen  that  two  feet  out  of  five  feet  of  the 
soil  was  open  space  which  could  be  occupied  with  water. 

159.  Maximum  Capillary  Capacity  of  Soils  for  Wp.ter. — 
The  amount  of  water  which  may  be  retained  in  soils  by 
capillarity  is  greatly  influenced  by  the  distance  of  the  soil 
above  standing  water  in  the  ground  and  by  the  frequency 
and  amount  of  rainfall.  The  cylinders  of  soil  referred  to 


\[Valcr  Capacity  of  Soils. 


133 


in  (158)  when  thoroughly  dried  and  then  placed  in  one 
inch  of  water  in  a  chamber  where  no  evaporation  could 
take  place,  took  up  and  retained  by  capillarity  the  follow- 
ing amounts  of  water : 

Table  showing  the  maximum  capillary  capacity  for  water  of 
field  soils  ruith  the  surface  11  inches  above  standing  water. 


Per  cent. 
of  water. 

Lbs.  of 
water  per 
cu.  ft. 

Inches  of 
water. 

32  2 

23  9 

4  59 

Second  foot  of  reddish  clay  contained  

23  8 

°2  2 

4  26 

24  5 

22  7 

4  37 

Fourth  foot  of  clay  and  sand  contained  

22  6 

22  ! 

4  95 

Fifth  foot  of  fine  sand  contained  

17.5 

19  6 

3  77 

Total... 

110.5 

21.24 

FIG.  41.— Apparatus  for  measuring  the  capillary  capacity  of  long  columns 

of  sand. 

It  is  clear  from  this  table  and  the  last  that  much  of  the 
pore  space  in  the  clayey  soils  cannot  be  maintained  full  of 
water  by  capillarity  even  when  the  surface  is  only  11  inches 
above  standing  water. 


134 


Physics  of  ike  Soil. 


160.  Influence  of  Distance  Above  Standing  Water  on  the 
Water  Capacity  of  Soils. — When  the  distance  to  the  ground- 
water  is  considerable  the  force  of  surface  tension  is  not 
great  enough  to  maintain  as  much  water  in  the  soil  as  when 
the  distance  is  less,  and  the  table  which  follows  shows  how 
the  amount  of  water  retained  varies  with  the  distance.  The 
sands  and  soils  were  placed  in  an  apparatus  represented  in 
Fig.  41,  arranged  so  as  to  permit  free  percolation  but  allow- 
ing very  little  evaporation  from  the  surface.  The  sand 
columns  were  8  feet  long  and  percolation  was  allowed  to 
continue  nearly  2.5  years.  The  soil  columns  were  7  feet 
long  and  percolation  from  them  was  continued  during  60 
days,  at  the  end  of  which  time  the  tubes  were  cut  into  short 
sections  and  the  amount  of  water  still  retained  determined 
by  drying. 

Percentage  distribution  of  water  left  in  columns  of  sand,  sandy 
loam  and  clay  loam  after  percolation  had  continued  two 
and  one-half  years  with  the  sand  and  60  days  with  the  soils. 


Height  of  section  above 
ground  water. 

Sand 
No.  20 

Sand 
No.  40 

Sand 
No.  60 

Sand 

No.  80 

Sand 
No.  100 

Sandy 
loam. 

Clny 
1  am 

Inches. 
96-93... 

Pr.  ct. 
0  27 

Pr.  ct 
0  17 

Pr.  ct 
0  22 

Pr.  ct. 
1  26 

Pr.  ct 
3  44 

Pr.  ct 

Pr.  ct. 

93-90  

.22 

.17 

.23 

1.16 

3  41 

90-87  

23 

16 

29 

1  34 

3  82 

87-84  

.22 

.15 

.32 

1  61 

3>3 

84-81  

23 

18 

61 

1  98 

3  93 

16.16 

21  .  18 

81-78... 

.29 

.19 

1  07 

2  32 

4.19 

78-75   

44 

26 

1  33 

2  61 

4  38 

16.08 

30  TO 

75-72  

89 

58 

1  57 

2  90 

4.92 

72-«9  

1  18 

16 

1  80 

3  12 

4  94 

16.55 

31.05 

69  66  

1  48 

45 

1  85 

3  36 

5.70 

66-63  

1  71 

67 

2  03 

3  56 

5  91 

16.97 

31.11 

63-60... 

1  80 

80 

2  18 

3  92 

6  43 

60-57  

1.83 

86 

2.26 

4.22 

6.77 

17.59 

31.21 

57-54  

1  93 

87 

2  27 

4  53 

7  72 

54-51  

1.98 

98 

2  30 

4  88 

8.59 

17.99 

31.  £4 

51-43  

2  02 

9° 

3  38 

5  42 

9  42 

48-4.i  

2  03 

2  12 

2  46 

6  03 

10.50 

18.70 

31.99 

4542  

2  02 

2  07 

2  71 

6  99 

11  34 

42-39  

2.06 

2  18 

3  08 

7  47 

12.68 

19.44 

32.18 

39-36  

2  17 

2  29 

3  46 

8  71 

13  00 

36-33  

2  31 

2  48 

4  10 

10  54 

14.95 

20.90 

32.45 

33-30  

2  36 

2  65 

?.09 

11  77 

15  90 

30-27  

2  63 

3.14 

6.36 

12.95 

17.20 

21.71 

33.31 

27-24  

2  86 

3  63 

X  74 

15  05 

17.96 

2t-2I  

3  42 

4  71 

13  52 

17  24 

18  92 

21.46 

34.40 

21-18    

4  26 

6  76 

23  57 

19  08 

20  49 

18-15  

6  41 

9  38 

27  93 

19  37 

21  34 

22.17 

35.51 

15  12  .. 

9  77 

14  66 

23  61 

21  44 

21  63 

12-  9  

16  08 

21  31 

22  46 

22  69 

22  68 

22.68 

35.97 

9-  6  

19  33 

22  39 

22  76 

2.1  20 

23  39 

6-  3  

20  96 

23  52 

22  88 

24  22 

30  28 

27.69 

37.19 

3-  Q..n  

21  58 

24  61 

23  54 

25  07 

21  08 

Water  Capacity  of  Soils. 


135 


This  table  shows  very  clearly  that  the  amount  of  water 
a  soil  can  retain  by  capillarity  is  very  materially  influenced 
by  the  distance  it  is  above  the  zone  of  complete  saturation 
or  of  standing  water  in  the  ground.  The  decrease  of  water 
upward  is  most  rapid  in  the  coarsest  sand  and  it  is  least 
rapid  in  the  finest  soil. 

It  is  remarkable  that  in  sands  so  coarse  as  those  used 
water  should  continue  to  drain  away  during  more  than  two 
years  from  so  short  a  vertical  column  and  that  so  small  an 
amount  of  water  was  retained  in  the  upper  sections  of  the 
columns.  It  is  not  probable  that  drainage  had  become 
complete  from  the  two  soils  although  it  may  possibly  have 
been,  as  there  was  no  percolation  during  the  last  five  days 
of  the  trial. 

161.  Proportion  of  Soil- Water  Available  to  Crops. — Not  all 
the  water  which  soils  will  retain  is  available  to  plants.  A 
certain  amount  must  be  left  overspreading  the  soil  grains 
which  the  roots  of  plants  are  unable  to  use.  The  amount 
found  in  one  field  soil,  when  corn  and  clover  ceased  to  grow 
and  when  the  leaves  curled  early  in  the  day,  is  given  in  the 
table  below.  In  the  same  table  is  also  given  the  moisture 
of  adjacent  fallow  ground  determined  at  the  same  time  and 
which  contains  the  least  amount  of  water  which,  for  this 
soil,  will  permit  maximum  crops. 

Soil  moisture  relations  when  growth  /.s  brought  to  a  standstill. 


Depth  of  samp"  ». 

Clover. 

Maize. 

Fallow 
ground. 

Per  cent. 
8.39 

Per  cent. 
6  97 

Per  cent. 
16.28 

8.48 

7.8 

17.74 

12-18  inch  reddish  clay..........  

12.42 

11.6 

19.88 

13.27 

11.98 

19.81 

13.52 

10.84 

18.56 

9.53 

4.17 

15.9 

The  moisture  contained  in  the  fallow  ground  shows  how 
much  this  type  of  soil  may  retain,  against  evaporation  and 
percolation,  during  a  dry  season,  and  it  happens  to  stand 


136 


Physics  of  the  Soil. 


just  at  the  under  limit  for  most  vigorous  growth  while  the 
upper  limit  is  given  in  the  next  table. 

Showing  upper  and  lower  limits  of  best  amount  of  soil  moist' 
ure  for  one  type  of  soil. 


Kind  and  depth  of  soil. 

Lower   limit 
of  soil 
moisture. 

Upper  limit 
of  soil 
moisture. 

Available 
soil 
moisture. 

Clay  loam,  first  foot  

Per  cent. 
17  01 

Per  cent. 

23  77 

Los.  per 
cu.  ft. 
6  92 

Reddish  clay,  second  foot  

19  86 

24  3 

4.112 

Sandy  clav,  third  foot  

18.55 

24.03 

5  722 

Sand,  fourth  foot  

15.9 

22.29 

6.786 

Total  

23.54 

It  will  be  seen  from  this  table  that,  to  bring  the  surface 
four  feet  of  soil  from  the  lower  limit  of  the  best  productive 
stage  of  water  content  to  the  upper  limit,  requires  an  ap- 
plication of  23.54  pounds  per  square  foot,  or  a  depth  of 
rainfall  equal  to  4.527  inches.  This  therefore  represents 
the  available  moisture  in  this  type  of  soil  and  is  about  one- 
third  of  its  full  capillary  capacity. 

162.  Kinds  of  Soil  Which  Yield  Their  Moisture  to  Crops 
Most  Completely. — When  the  roots  of  plants  come  to  draw 
upon  the  supply  of  soil-water  those  soils  yield  their  mois- 
ture to  the  plant  most  completely  whose  grains  have  the 
largest  diameter  or,  more  precisely,  which  have  the  smallest 
internal  surface  to  which  the  moisture  may  adhere  and  over 
which  it  is  spread. 

Referring  to  the  table  in  (161),  giving  the  per  cents,  of 
moisture  which  were  too  low  to  permit  the  plants  to  supply 
their  needs,  it  will  be  seen  that  under  the  corn  the  water  in 
the  sand  had  been  drawn  down  to  about  4  per  cent. ;  in  the 
surface  loam  to  7  and  8  per  cent. ;  while  in  the  intervening 
more  clayey  portion  only  to  11  and  12  per  cent.  The  fun- 
damental truth  which  should  be  grasped  here  is  that  all 
these  soils  are  equally  dry  so  far  as  the  needs  of  the  corn 
crop  are  concerned,  and  one  of  the  reasons  why  they  are 


Water  Capacity  of  Soils.  137 

so  is  because  the  thickness  of  the  water  film  surrounding 
the  grains  is  nearly  the  same  in  all  the  cases. 

The  truth  of  this  statement  will  be  evident  if  we  com- 
pute the  per  cent,  of  moisture  in  a  soil  which  a  given  thick- 
ness of  film  surrounding  the  grains  will  produce. 

163.  Relation  of  Thickness  of  Moisture  Films  to  Per  Cent. 
of  Soil  Moisture.—  If  the  data  in  the  table  of  (145)  is  used 
the  per  cent,  of  soil  moisture  a  given  thickness  of  film  will 
produce  may  be  computed  approximately  from  the  formula 


where  P  =  the  per  cent,  of  moisture  in  the  soil. 
K=  a  factor,  Log.  5.497532  =  .0314355 
S  =  surface  of  soil  per  cu.  ft.  taken  from  (145) 
T  =  thickness  of  film  of  moisture 

Q  =  per  cent,  of  dry  soil  obtained  by  subtracting  the  pore 
space  in  (145)  from  100. 

Using  this  formula  and  the  data  in  (145)  it  will  be 
found  that  the  per  cents,  of  moisture  stand  as  given  below  : 
With  thickness  of  film  nroVsW  inch  the  per  cent,  of  water 
will  be,  in  the 

Heavy  red  clay  ..........................  14  .24  per  cent. 

Loamy  clay  ..............................  12.00  per  cent. 

Loamy  clay  ..............................  8.  74  percent. 

Loam  ....................................  7.20  per  cent. 

Sandy  loam  ..............................  5.21  percent. 

Sandy  soil  ...............................  2.09  per  cent. 

Sandy  soil  .........  ......................  1.41  per  cent. 

Coarse  sandy  soil  ........................  1  .  11  per  cent  . 

From  this  table  it  will  be  seen  that  the  coarse  sandy  soil 
contains  only  1.1  per  cent,  of  its  dry  weight  of  moisture 
when  the  heavy  red  clay  contains  14  per  cent,  with  the  same 
thickness  of  film  surrounding  the  soil  grains. 

Comparing  these  per  cents,  of  moisture  with  ihose  con- 
tained in  the  soil  in  which  the  corn  wilted,  it  will  be  seen 
that  the  sand  of  that  soil  was  really  the  wettest  soil  there,  so 
far  as  the  available  moisture  is  concerned,  there  being  at 


138  Physics  of  the  Soil. 

least  2  per  cent,  of  moisture  yet  available.  The  loamy 
clay  of  (145),  and  given  in  the  table,  has  about  the  same 
texture  as  that  of  the  reddish  clay  in  the  table  of  (161)  and 
it  will  be  seen  that  its  per  cent,  of  moisture  under  the  corn 
was  also  about  the  same  as  that  computed. 

164.  Available  Soil-Moisture  Affected  by  Jointed  Structure 
in  Clay  Subsoils. — The  tendency  of  clay  subsoils  to  shrink 
and  become  divided  into  small  cube-like  blocks  greatly  di- 
minishes the  available  moisture  in  them.     This  shrinkage 
not  only  often  i-esults  in  breaking  rootlets  in  two  but  when 
new  rootlets  form  they  advance  most  readily  through  the 
fissure  planes  and  are  not  able  to  place  themselves  in  the 
most  favorable  relations  with  the  soil  to  permit  capillarity 
to  bring  the  moisture  to  the  rootlets.     It  is  because  the 
sandy  soils  and  loams  seldom  develop  the  structure  referred 
to  and  because  the  rootlets  and  root  hairs  are  able  to  secure 
a  more  uniform  distribution  throughout  them  as  well  as 
because  of  the  larger  size  of  their  grains  that  plants  are  able 
to  drain  their  moisture  down  to  so  low  a  per  cent. 

165.  Available  Soil-Moisture  Increased  by  Open  Structure. 
— When  soils  are  in  any  way  left  with  a  loose  open  struc- 
ture, as  happens  with  deep  plowing  and  especially  with 
good  subsoiling,  not  only  is  the  ability  of  the  loose  soil  to 
retain  moisture  increased  but  a  larger  proportion  of  this 
retained  water  becomes  available  to  the  crop.       A  larger 
amount  of  water  is  retained  because  when  perfect  capillary 
connection  with  the  unstirred  soil  below,  is  broken,  surface 
tension  opposes  rather  than  aids  gravity  in  producing  per- 
colation and  spaces  too  large  to  remain  full  of  water  other- 
wise are  able  to  retain  it. 

When  the  soil  is  open  and  loose  the  case  is  quite  different 
from  that  resulting  from  shrinkage  referred  to  in  (164), 
for  in  this  case  the  roots  and  root  hairs  are  better  able  to 
enter  the  separated  portions  and,  as  the  moisture  films  are 
thicker,  the  moisture  is  more  readily  gathered. 


Amount  of  Water  Required  by  Crops. 


139 


166.  Drainage  May  Increase  the  Available  Soil-Moisture. — 
When  the  subsoil  is  too  close  and  too  fully  saturated  with 
water  to  permit  the  roots  of  crops  to  penetrate  it,  as  is  the 
case  where  drainage  is  needed,  the  roots  of  plants  are  forced 
to  develop  in  so  limited  an  amount  of  soil  that  when  a  dry- 
ing time  conies,  and  when  the  demands  of  the  crops  for 
moisture  are  large  because    of  rapid  growth,    capillarity 
from  below  is  not  able  to  supply  the  moisture  as  fast  as 
needed,  and  the  result  is  the  zone  of  soil  occupied  by  the 
roots  becomes  so  dry  that  growth  is  impeded. 

On  the  other  hand,  where  a  field  is  well  drained  the  roots 
are  extended  through  much  larger  volumes  of  soil ;  the  lo- 
cal demands  are  thus  less  urgent  and  the  water  need  not 
move  so  far  by  capillarity  before  the  plant  comes  in  pos- 
session of  it.  Under  these  conditions  the  moisture  of  the 
surface  four  feet  of  soil  is  in  close  reach  of  the  roots  and 
capillarity  may  still  add  to  this  supply  from  below. 

167.  The  Amount  of  Water  Required  by  Crops. — It  has 
been  determined  by  careful  and  extended  observations  in 
this  country  and  in  Europe  that  almost  any  one  of  the  cul- 
tivated crops  withdraws  from  300  to  500  tons  of  water  from 
the  soil  for  each  ton  of  dry  matter  produced.     In  Wiscon- 
sin the  amounts  of  water  lost  from  the  soil  by  evaporation 
during  the  growing  season  and  through  the  plant  are  given 
in  the  table  below : 

Table  showing  the  mean  amount  of  water  used  by  various 
plants  in  Wisconsin  in  producing  a  ton  of  dry  matter. 


Water 

Acre-in.  of 

No.  of 
trials. 

used  per 
ton  of  dry 

Water 
used. 

Dry  matter 
per  acre. 

water  per 
ton  of  dry 

matter. 

matter. 

Tons. 

Inches. 

Tons. 

Barley  

5 

464.1 

20  69 

5  05 

4  096 

Oats  

20 

503.9 

39  53 

8.89 

4.447 

Maize  

52 

270.9 

15  76 

6  59 

2  391 

Clover  

46 

576.6 

22  34 

4.39 

5.089 

1 

477.2 

16  89 

4  009 

4  212 

Potatoes  

14 

385.1 

23.78 

6  995 

138 

Av.  446.3 

23,165 

5.987 

3.939 

140 


Physics  of  the  Soil. 


From  this  table  it  is  seen  that  the  amount  of  water  used 
ranges  from  270  tons  of  water  with  corn  to  576  tons  with 
clover  per  ton  of  dry  matter ;  or  when  expressed  in  acre- 
inches  from  2.4  to  5.1  inches  nearly,  the  average  for  the 
six  crops  being  nearly  450  tons  or  4  acre-inches  per  ton  of 
dry  matter. 

When  the  yields  per  acre  are  2,  3  and  4  tons  the  num- 
bers given  above  must  be  multiplied  by  the  same  factors. 

168.  Amounts  of  Water  Required  for  Different  Yields  of 
Wheat. — In  order  to  express  the  data  of  the  last  section  in 
terms  which  it  is  more  customary  to  use,  there  is  given  in 
the  next  table  the  amount  of  water  required  by  a  crop  of 
wheat  when  the  yields  per  acre  range  from  15  to  40  bushels. 

Observations  made  by  Hellriegel  in  Germany  show  that 
wheat  uses  about  453  tons  or  3.998  acre-inches  of  water 
for  a  ton  of  dry  matter.  Using  this  ratio  and  one  pound 
of  grain  to  1.5  pounds  of  straw  the  water  required  will 
*f and  as  below : 


Table  showing  the  least  amount  of  water  required  to  produce 
different  yields  of  wheat  per  acre  when  the  ratio  of  grain 
to  straw  is  I  to  1.5. 


YIELD  PEE  ACRE. 

Water  used. 

Number  of  bushels.  . 

Weight  of 
grain. 

Weight  of 
straw. 

Total  weight 

15... 

Tons. 

.45 
.60 
.75 
.90 
1.05 
1.20 

Tons. 

.675 
90 
1  125 
1.350 
1.575 
1.800 

Tons. 

1.125 

1.500 
1.575 
2.*50 
2.625 
3. 

Acre-  inch. 

4  498 
5.998 
7.497 
8.997 
10.495 
12. 

20... 

25  

ao... 

85... 

40  

This  table  shows  that  12  inches  of  effective  rain  during 
the  growing  season  of  wheat,  starting  with  the  soil  moisture 
in  good  condition,  should  enable  a  yield  of  40  bushels  per 
acre  to  be  produced. 


Amount  of  Water  Required  by  Crops. 


141 


1G9.  least  Amount  of  Water  Which  Will  Permit  Yields 
of  Different  Amounts. — In  the  next  table  there  is  given  the 
least  amount  of  water  taken  from  the  soil  which  can  be  ex- 
pected to  give  the  yields  for  the  different  crops  there  stated : 

This  table  must  be  regarded  as  showing  the  minimum 
amounts  of  water  which  will  bring  the  crops  named  to 
full  maturity  so  as  to  produce  the  yields  specified  under 
conditions  of  absolutely  no  loss  by  surface  or  under-drain- 
age,  and  where  the  evaporation  from  the  soil  itself  is  aa 
small  as  it  can  well  be.  It  must  be  farther  understood  that 
the  soil  at  seeding  time  already  possesses  the  needful 
amount  of  water  for  the  best  conditions,  and  that  at  the 
end  of  the  growing  season  it  is  yet  so  moist  that  no  check 
to  vigorous,  normal  growth  has  occurred. 

Table  showing  the  highest  probable  duty  of  water  for  differ- 
ent yields  per  acre  of  different  crops. 


Bushels  per  acre 

15 

20 

30 

40 

50 

60 

70 

80 

100 

200 

300 

400 

Name  of  crop. 

Least  number  of  acre-inches  of  water. 

Wheat  

4.5 

3.21 
2.35 
2.  52 

6 
4  28 
3.136 
3.36 
.41 

9 
6.42 
5  701 
5.31 
.62 

12 

8.56 
6.27J 
6.72 
.83 

15 
10.7 

7  81 
8.4 
1.03 

18 
12.84 
9.40 
10.08 
1.24 

19  98 
10.98 
11.75 
1.45 

Oats  

12.54 
13.43 
1.65 

15.6J- 
16.77 
2.07 

Maize  

I'.U 

'6.2 

'8"27 

Tons  per  acre.  .. 

1 

2 

3 

4 

6 

8 

10 

12 

14 

16 

18 

£0 

Least  number  of  acre-inches  of  water. 

Clover  hay,  15 
per  cent,  water 
Corn  with  ears, 
15  perct.  water 
Corn  silage,  70 
percent,  water 

4.43 
2.08 
1.41 

8.85 
4.16 

2.82 

13.28 
6.24 
4.23 

17.7 
8.32 
5.64 

26.55 
12.47 
8.46 

35.4 
16.61 
11.23 

14.25 
20.72 
14.1 

24.95 
16.92 

29.1 
19.74 

33.26 
22.56 

37.42 
25.38 

41.58 
28.2 

CHAPTER     VI. 
PHYSICS  OF  PLANT  BREATHING  AND  ROOT  ACTION. 

MECHANISM   AND   METHOD   OF   TRANSPIRATION    IN    PLANTS. 

170.  Breathing  of  Plants  and  Animals. — The   transpira- 
tion of  plants  and  the  respiration  of  animals  are  processes 
which  have  much  in  common.     Both  plants  and  animals 
are  provided  with  internal  cavities  into  which  air  may  en- 
ter.    They  both  breath  air.    While  breathing  air  both  give 
off  large  quantities  of  moisture.  The  primary  object  of  the 
lungs  is  to  supply  the  body  of  the  animal  with  oxygen  and 
to  remove  carbon  dioxide.    The  corresponding  structure  in 
the  leaves  of  plants  is  to  supply  it  with  carbon  dioxide  and 
to  throw  off  oxygen.     In  both  cases  the  breathing  surface 
has  a  very  delicate  texture  and  is  situated  where  it  can  al- 
ways be  kept  wet;  the  chief  function  of  the  water  escaping 
from  the  breathing  surface  is  to  keep  it  moist. 

If  the  lining  of  the  lungs  were  to  become  dry  and 
parched  the  gases  would  not  as  readily  pass  through  and 
there  would  be  like  difficulty  in  the  case  of  leaves,  if  their 
breathing  surfaces  were  not  kept  moist.  In  both  plants 
and  animals  the  breathing  surfaces  are  carefully  guarded 
from  the  intense  sun  and  strong  drying  winds. 

171.  Respiratory  Organs  in  Plants. — The  air  passages  or 
breathing  chambers  of  plants  are  chiefly  located  in  the 
leaves,  but  they  are  also  found  to  greater  or  less  extent  in 
all  the  green  parts.     They  are  simply  irregular  chambers 
left  between  the  cellular  tissue  and  are  represented  in  the 


Respiration  and  Transpiration  of  Plants.          143 

lower  portion  of  Fig.  42,  which  shows  a  section  of  barley 
leaf  with  the  epidermis  removed  and  much  magnified. 

172.  Breathing  Pores. — Leading  into  the  air  chambers 
are  many  breathing  pores  through  which  the  air  enters. 

Eight  of  these  are  repre- 
sented in  Fig.  42.  They 
are  most  numerous  on  the 
under  sides  of  leaves 
where  evaporation  may  be 
least. 

The  breathing  pores  or 
stomata  are  very  small 
and  numerous,  Weiss  es- 
timating, from  an  average 
of  40  plants,  as  many  as 
209,000  in  each  square 
centimeter  of  surface,  an 
area  equal  to  the  square 
shown  in  Fig.  43.  In 
the  case  of  a  corn  leaf 
21  per  cefit.  of  the  surface 

FIG.  42— Structure  of  barley  leaf.      fAfteria    nr>r>iTmprl    Kv    flip    rlnnr- 
Sorauer;  sp  is  a  breathing  pore ;  m,  chlo- 1S  "J    ] 

rophyll  cells ;  i,  respiratory  chambers,     ways      to      the      breathing 

chambers. 

173.  Chlorophyll  Cells. — Surrounding  the  air  chambers 
in  every  leaf  there  are  multitudes  of  tender,  thin-walled 
cells  in  which  are  found  the  green  chlorophyll  grains,  giv- 
ing color  to  the  leaf,  which  absorb  the  sunshine  and  use  it 
in  breaking  down  the  carbon  dioxide  for  the  carbon,  which 
is  one  of  the  chief  constituents  of  plant  tissues,  and  of  the 
starches,  sugars  and  most  other  compounds. 

174.  Guard  Cells. — In  order  that  the  loss  of  water  may  be 
as  little  as  possible  each  breathing  pore  is  surrounded  by  a 
pair  of  guard  cells,  represented  in  Fig.  42,  and  on  a  much 
larger  scale  in  Fig.  43.     These  guard  cells  have  for  their 
function  the  regulation  of  the  amount  of  evaporation  from 


Physics  of  the  Soil. 


the  plant.     The  chlorophyll  grains  can    be    effective    in 
breaking  down  the  carbon  dioxide  only  in  comparatively 


FIG.  43.— Diagram  showing  the  mechanical  action  or  guard  cells  In  open 
ing  and  closing  breathing  pores.  The  square  shows  the  area  of 
under  side  of  leaf  containing  an  average  of  209,000  breathing  pores 
or  stomata.  (From  Irrigation  and  Drainage.) 

bright  light  and  so,  during  cloudy  days  and  at  night,  the 
guard  cells  automatically  change  their  form  and  close  the 
doors,  reducing  evaporation.  Indeed  they  remain  open 
only  when  there  is  light  enough  to  utilize  it  in  decomposing 
the  carbon  dioxide. 

175.  Action  of  the  Guard  Cells. — The  opening  and  closing 
of  the  guard  cells  is  brought  about  by  their  peculiar  shape 
and  changes  in  the  amount  of  material  they  contain. 

Unlike  the  other  cells  in  the  epidermis  of  the  leaf  these 
contain  chlorophyll  grains  and  are  thus  able  to  carry  on  the 
process  of  developing  plant  food.  The  advantage  of  hav-- 
ing  this  work  done  here  is  to  increase  the  osmotic  pressure 
through  the  rendering  of  the  sap  denser  when  the  sun  is 
shining,  thus  distending  the  cells  and  changing  their  shape 
BO  as  to  open  the  doors  widest  when  the  sun  shines  brightest, 
as  represented  at  A,  Fig.  43.  When  night  comes  or  it  is 
cloudy  then  the  osmotic  pressure  forces  the  assimilated  ma- 
terial out  of  the  guard  cells  faster  than  it  is  produced  and 
the  walls  collapse,  taking  the  attitude  represented  at  C  and 
in  cross  section  at  D,  closing  the  opening.  B  and  D  are 
cross  sections  of  a  pair  of  guard  cells  along  the  lines  1-2 
and  B  shows  how  a  full  cell  must  pull  the  edges  apart  while 


Root  Action  in  Plants.  145 

D  shows  how  the  limp  condition  will  permit  the  walls  to 
fall  together. 

176.  loss  of  Water  Through  the  Guard  Cells. — The  epi- 
dermis of  the  leaf  is  so  close  in  texture  and  often  so  water- 
proofed that  when  the  guard  cells  close  there  is  but  little 
loss  of  moisture.  But  when  the  sun  shines  and  there  is 
moisture  enough  in  the  soil  to  keep  the  leaves  from  wilting 
the  guard  cells  open  wide  and  great  evaporation  may  take 
place  even  in  a  saturated  atmosphere. 

By  admitting  live  steam  into  our  plant  house  on  bright 
sunny  days,  keeping  the  air  highly  saturated,  we  have 
found  corn  to  lose  nearly  as  much  moisture  as  in  the  dryer 
condition  of  the  air  with  the  sun  also  shining.  The  reason 
this  is  possible  is  that  the  epidermis  acts  like  the  glass  of 
the  hot  bed,  permitting  the  sunshine  to  enter  but  preventing 
the  longer  dark  heat  waves  from  escaping.  In  this  way 
the  air  saturated  outside  is  not  so  inside  on  account  of  the 
higher  temperature.  This  remarkable  provision  of  the 
plant  to  save  moisture  should  teach  how  important  it  is  to 
assist,  in  every  way  practicable,  the  conservation  of  soil 
moisture. 


STRUCTURE  AND  MODE  OF  ROOT  ACTION". 

There  is  scarcely  a  better  illustration  anywhere  in 
Nature  of  the  adaptation  of  living  organisms  to  their  en- 
vironments than  is  furnished  by  the  mechanism  by  which 
the  higher  land  plants  supply  themselves  with  moisture; 
and  one  of  the  most  remarkable  of  remarkable  tasks  is  that 
of  a  corn  plant  pumping  into  its  stem  and  leaves,  from  a 
comparatively  dry  soil,  2.896  pounds  of  water  daily  for  13 
consecutive  days. 

177.  Functions  of  Roots — The  roots  of  ordinary  land 
plants  have  three  distinct  functions  to  perform:  First,  to 
gather  from  the  soil  its  moisture  and  the  salts  dissolved  in 
it  for  the  use  of  the  plant;  second,  to  convey  and  deliver 


146 


Physics  of  the  Soil. 


into  the  stem  and  leaves  the  water  absorbed ;  and  third,  to 
act  as  an  anchor  or  support,  holding  the  plant  upright  in 
the  soil,  air  and  sunshine. 


Fid.  44.— A,  Root-hairs  of  mustard  plants,  with  soil  adhering,  and  with 
soil  removed.  B.  root-lmirs  of  wheat,  when  very  young,  and  four 
weeks  later.  (After  Sachs.) 

178.  The  Absorbing  Portion  of  Roots — It  is  the  general 
belief  of  plant  physiologists  that  the  active  portion  of  roots 
— that  which  is  immediately  concerned  in  gathering  the 
water  from  the  soil — is  what  are  known  as  root  hairs,  rep- 
resented at  the  left  of  A,  Fig.  44,  and  at  A  buried  in  the 
soil  grains  in  the  same  figure.  In  Fig.  46  is  a  much  en- 
larged view  of  a  single  root  hair  which  has  worked  its  way 
in  among  the  soil  grains  where  it  is  in  place  to  absorb  soil 
moisture  and  soluble  salts.  The  appearance  of  root  hairs 
in  relation  to  soil  grains  can  be  clearly  demonstrated  by 
growing  plants  in  rather  coarse  sand  between  glass  plates 
as  represented  in  the  apparatus  shown  in  Fig.  45. 


Root  Action  in  Plants. 


147 


179.  Structure  of  Root  Hairs. — Boot  hairs  are  extremely 
thin  walled  and  greatly  lengthened  single  cells,  having 
lengths  ranging  up  to  an  eighth  or  quarter  of  an  inch  and 

a  diameter  of  TOU  of  an 
inch.  They  stand  out 
about  the  main  root  like 
the  pile  of  velvet,  forming 
a  brush-like  appearance 
as  shown  in  Fig.  44.  The 
object  of  this  form  is  to 
secure  a  large  area  around 
which  surface  tension 
may  force  the  water  in 
the  same  way  that  it  does 
about  the  soil  grains.  In- 
deed root  hairs  have 
forms  adapted  to  drawing 
upon  themselves  a  portion 
of  the  water  film  invest- 
ing the  soil  grains. 

180.  Relation    of    Root 
Hairs  to  Soil  Grains. — The 
manner     in    which     root 
.  ,  hairs      place     themselves 

Fio.45.— Apparatus  for  observing  the  growth  f.  ., 

of  roots  and  their  relation  to  soil  grains.  amonST    tne    SOli    grains    13 
The  sides  of  the  apparatus  are  two  panes    n         i        T  •      7i         /• 

of  glass,  1.5  inches  apart.  cleariy  shown  in  the  form 

of  a  diagram  in  Fig.  46  where  h  h  is  a  root  hair ;  e  is  the 
main  root,  2  a  soil  granule,  and  1  an  air  space;  while  the 
concentric  lines  represent  the  films  of  capillary  moisture 
which  surround  both  the  granules  and  the  root  hairs.  In 
Fig.  47  is  represented  the  tip  of  a  young  growing  root  ad- 
vancing into  fresh  soil  and  having  five  root  hairs  developed 
in  place  among  the  soil  grains  ready  for  work. 

181.  Method  by  which  Root  Hairs  Gather  Water — As  the 
root  hairs  force  their  way  through  the  pore  spaces  among 
the  soil  granules  they  bring  their  walls  into  close  touch  with 


148  Physics  of  the  Soil. 

them  in  such  a  way  that  in  form  and  position  they  make 
up  a  part  of  the  soil  mass.  In  this  relation  the  force  of 
adhesion  draws  the  capillary  water  out  over  their  walls  so 


FIG.  46.— Distribution  of  water  on  the  surfaces  of  soil  grains  and  of 
root-hairs,  e,  main  root:  1,  air  space;  2,  soil  grain;  3,  nlni  of  water; 
h  h,  root-hairs.  (After  Sachs.) 

as  to  leave  them  and  the  soil  granules  surrounded  by  the 
water  film.  Each  root  hair  is  or  should  be  in  a  sense  under 
water,  that  is  invested  in  a  film  of  greater  or  less  thickness. 
When  a  portion  of  this  water  enters  the  root  hair  and 
passes  on  into  the  root  and  up  to  the  leaves,  the  water  layer 
surrounding  the  root  hair  is  left  thinner;  but  no  sooner 
does  this  thinning  out  occur  than  the  equilibrium  is  de- 
stroyed and  surface  tension  at  once  squeezes  more  water 
onto  the  surface  from  the  surrounding  soil.  In  this  way 
capillarity  keeps  the  water  moving  to  the  root  hairs  as  they 
pass  it  on  to  the  plant. 

182.  Advance  of  Eoots  through  the  Soil. — Until  the 
method  by  which  roots  advance  through  the  soil  is  under- 
stood it  is  difficult  to  realize  how  it  is  possible  for  such  deli- 
cate structures  to  set  the  heavy  soil  aside  sufficiently  to 
reach  the  great  depths  they  do.  Nature's  method  of  over- 
coming the  difficulty  is  simple  enough  and  it  is  as  effective 
as  it  is  simple.  The  large  amount  of  open  space  there  is  in 
the  surface  four  to  six  feet  of  soil  makes  it  easier  to  set  the 


Root  Action  in  Plants. 


149 


soil  aside,  and  the  setting  of  fence  posts  proves  how  large 
this  space  is.  A  6-inch  post  set  in  the  hole  dug  for  it  seldom 
occupies  so  much  of  tho  space  but  that  all  of  the  soil  re- 
moved may  be  returned  by  thorough  ramming.  It  is  the 
existence  of  such  large  amounts  of  open  space  in  the  soil 
which  makes  the  movements  of  water,  air  and  roots 
through  it  possible  and  the  absence  of  it  which  makes  a 
puddled  soil  so  uncongenial  to  plant  growth. 


FIG.     47.— Methc 


jy     which     root-hairs     advan< 
(Adapted   from   Sachs.) 


jugh     the     solL 


In  Fig.  47  is  represented  a  section  of  the  tip  of  a  root 
growing  and  advancing  through  the  soil.  It  has  been 
found  that  at  1,  a  short  way  back  from  the  tip,  there  is  a 
center  of  growth.  Here  new  cells  are  forming  by  division 
and  subsequent  enlargement.  On  the  forward  side  of  this 
cell  the  new  ones  build  the  root  cap,  which  acts  as  a  shield 
and  wedge,  while  those  in  the  rear  are  finally  transformed 
to  make  the  various  structures  found  in  the  root. 

At  the  center  of  growth  new  cells  are  forming  and  ex- 
panding under  the  intense  power  of  osmotic  pressure  and, 
as  the  root  is  anchored  behind,  the  root  cap  is  pushed  for- 
10 


150  Physics  of  the  SoiL 

ward  and  wedged  sidewise,  setting  the  soil  aside  and  tlni3 
making  room  for  itself.  The  root  cap  does  not  slide  for- 
ward past  soil  grains  but  is  anchored  rigidly  to  them ;  the 
tip  entering  existing  cavities  is  enlarged  by  growing  for- 
ward under  and  through  the  cap,  the  rear  cells  of  which  die 
after  the  root  has  grown  past  them,  the  root  cap  being  a  sor« 
of  point  continually  renewed  as  the  root  advances. 

183.  The  Extent  of  Root  Development  of  Corn. — It  is  only 
by  careful  study  that  the  extent  of  root  development  in  a 
soil  can  be  learned.     In  Figs.  48  and  49  are  shown  the 
amount  and  distribution  of  corn  roots  at  two  stages  of 
growth.     When  the  corn  was  30  inches  high  the  whole  of 
the  soil  to  a  depth  of  two  feet  was  as  full  of  roots  as  the 
engraving  shows  between  the  two  hills ;  when  the  corn  was 
coming  into  tassel  the  roots  had  penetrated  to  a  depth  of 
three  feet  and  had  come  closer  to  the  surface ;  and  at  ma- 
turity the  roots  had  reached  four  feet  in  depth,  making 
their  way  through  a  fairly  heavy  clay  loam  and  clay  sub- 
soil, the  fourth  foot  only  being  sandy. 

It  should  be  understood  that  the  roots  here  shown  grew 
in  undisturbed  field  soil  and  were  obtained  by  going  into 
the  field  at  the  stage  of  growth  shown  and  digging  a  trench 
around  a  block  of  soil  a  foot  through  and  the  length  of  the 
width  of  the  row.  The  cage  was  then  set  down  over  the 
block ;  wires  run  through  the  block  of  soil  to  hold  the  roots 
in  place  and  then  the  soil  washed  away  by  pumping  water 
in  a  fine  spray  upon  the  block.  Three  days'  work  for  two 
men  were  required  to  secure  the  sample  in  Fig.  49. 

184.  Extent  of  Root  Development  of  Grain. — In  Fig.  50 
is  represented  the  depth  to  which  the  roots  of  winter  wheat, 
barley  and  oats  penetrated  a  heavy  clay  soil  and  subsoil. 
The  roots  are  what  were  found  in  a  cylinder  of  soil  just 
one  foot  in  diameter  and  were  obtained  by  driving  a  cylii. 
der  of  metal  four  feet  long  its  full  depth  into  the  soil  and 
then  washing  the  dirt  out  of  it.     It  will  be  seen  that  in  each 
case  the  roots  have  reached  a  depth  of  fully  four  feet. 


Hoot  Action  in  Plants. 


151 


FIG.   48.— Showing   amount   and   distribution   of   corn   roots   under   natural 

field   conditions. 


152  Physics  of  the  Soil. 


FIG.  49. — Showing  amount  and  distribution  of  corn  roots  under  natural 
field  conditions. 


Root  Action  in  Plants. 


153 


Wheat. 


Barley. 


Oats. 


FIG.  50.— Showing  amount  of  roots  found  in  the  field  in  cylinder  of  soil 
one  loot  in  diameter,  extending  to  a  depth  of  four  feet. 


154 


Physics  of  the  Soil. 


FIG.  51.— Showing  the  total  root  of  one  hill  of  corn. 


Root  Action  in  Plants. 


155 


PIG.  B2.— Showing  total  roots  of  oats. 


15.6 


Physics  o£  iltie  Soil. 


FIG.  53.— Showing  total  roots  of  medium  clover. 


Extent  of  Root  Growth.  157 

The  coarse  branches  shown  with  the  winter  wheat  roots 
are  the  roots  of  a  red  oak  tree  which  was  growing  in  a 
pasture  33  feet  away,  and  they  serve  to  show  how  far  forest 
trees  send  their  roots  foraging  through  the  soil  for  water 
and  food,  and  through  ,what  long  lines  the  water  must  be 
pumped  after  it  has  been  gathered. 

185.  The  Total  Root  of  Plants. — In  the  preceding  sections 
the  samples  simply  show  the  amount  of  root  found  in  a 
given  volume  of  field  soil.  In  Fig.  51  is  shown  the  total 
root  of  four  stalks  of  corn,  while  Figs.  52  and  53  show  the 
same  thing  for  oats  and  medium  clover.  These  were  se- 
cured by  growing  the  plants  in  cylinders  42  inches  deep 
and  18  inches  in  diameter,  filled  with  soil.  When  the 
crops  were  mature  the  cylinders  were  cut  down  and  the  soil 
washed  away. 

In  each  case  the  roots  extended  to  the  bottoms  of  the 
cylinders,  forming  a  dense  mat  there,  as  the  engravings 
show. 

The  roots  shown  with  the  clover,  and  which  gathered  the 
moisture  for  the  top,  forced  from  the  soil  water  enough  to 
cover  the  space  to  a  depth  of  2-9  inches.  It  will  be  seen 
that  the  stand  of  clover  is  very  close,  fully  three  times  as 
heavy  as  a  good  clover  crop  in  the  field;  This  was  made 
possible  by  having  a  rich  soil  and  supplying  all  the  water 
the  plant  could  use  at  just  the  right  time. 

The  length  of  all  these  roots  is  less  than  it  would  have 
been  had  the  cylinders  been  deeper,  as  proven  by  the  mat- 
ting at  the  bottom. 


CHAPTEK  VIL 

MOVEMENTS  OF  SOIL  MOISTTTEE, 

186.  Types  of  Soil  Moisture  Movement. — The   moisture 
which  is  found  in  the  soil  above  the  surface  of  the  ground 
water  is  continually  subjected  to  three  types  of  movement: 
(1)  Gravitational,"  (2)  Capillary  and  (3)  Thermal;  the, 
first  due  to  the  action  of  gravity^  the  second  to  surface  ten- 
sion and  the  third  to  heat. 

When  rain  falls  upon  the  soil  one  portion  of  it  begins 
to  flow  vertically  downward  through  the  pore  spaces,  urged 
to  do  so  by  the  pull  of  gravity ;  a  second  portion  increases 
the  thickness  of  the  water  film  surrounding  the  soil  grains 
and  root  hairs  and  is  made  to  do  so  by  surface  tension; 
while  a  third  portion  is  returned  to  the  atmosphere  through 
evaporation,  caused  by  heat. 

GRAVITATIONAL  MOVEMENTS. 

187.  Percolation  of  Soil  Moisture. — The  direct  gravita- 
tional flow  of  soil  moisture,  which  occurs  during  and  after 
rains,   is   nearly   always   vertically   downward   until   the 
ground-water  surface  is  reached.       The  movement  takes 
place  chiefly  through  the  shrinkage  cracks  and  passage- 
ways left  by  the  decay  of  roots  and  the  burrowing  of  ani- 
mals, but  also  through  the  capillary  pores  formed  by  the 
grains  of  the  coarser  soils  and  by  the  granules  of  the  finer 
types. 

The  rate  of  movement  is  most  rapid  following  heavy 
rains  when  the  soil  is  already  well  saturated.  After  pro- 
longed periods  of  drought,  when  the  soil  has  become  very 
dry,  there  is  so  much  air  in  the  pore  spaces  that  it  greatly 


Rate  of  Percolation  of  Soil  Water. 


159 


impedes   percolation    except   in    those    cases    where   wide 
shrinkage  checks  and  cracks  have  resulted. 

Where  percolation  is  influenced  chiefly  by  soil  texture  it 
is  most  rapid  through  the  sandy  soils  and  the  more  granu- 
lated clay  types.  It  is  least  rapid  through  the  puddled 
clays. 

188.  Rate  of  Percolation  Through  Sands. — When  the  sim- 
ple sands  are  once  completely  filled  with  water  the  perco- 
lation from  them  is  quite  rapid  but  decreases  with  the  size 
of  the  sand  grains.  In  the  table  below  is  given  the 
amount  of  water  which  percolated  from  the  columns  of 
sand  referred  to  in  (160). 

Table  giving  the    rate  of  percolation  from  sands    under  the 
gravitational  head  of  the  inclosed  water. 


GRADE  OF  SAND. 

Effective 
diameter 
of  grain. 

Per  cent 
of  pore 
space. 

Weight 
of  sand 
per  8  cu- 
bic feet. 

AMOUNT  OF  WATEE  PKRCO- 

LATtD  IN  — 

First  30  min. 

Second  30  min. 

No.  20..., 

ra.  m. 

0.4745 
.1818 
.1551 
.1183 
.08265 

38.83 
40.07 
40  76 
40.57 
39.73 

Pounds. 

809.28 
79.J.28 
784.00 
786.61 
797.76 

Lbs. 

53  33 
30.27 
29.99 
7.86 
6.31 

Inches. 

10.95 
7.519 
5  671 
1.512 
1  213 

Lbs. 

21.  ?6 
27.  H5 
23  f2 
6.73 
4.40 

Inches. 

46S3 

5.2.iS 
4.W2 
l.'JtU 
.815 

No.  40  

No.  ft)  

No.  fcO  

No.  100  

It  will  be  seen  from  the  above  table  that  the  rate  at  which 
the  water  moved  downward  through  the  coarsest  or  No.  20 
sand  was  such  as  to  average  during  the  first  thirty  minutes 
492  inches  per  twenty-four  hours,  while  for  the  finest  or 
No.  100  sand  the  mean  rate  was  58.16  inches,  the  flow 
from  the  first  being  nearly  8.5  times  as  fast,  with  grains 
not  quite  6  times  as  large. 

After  the  end  of  the  first  nine  days  of  percolation  these 
coarse  sands  lost  about  1.7  per  cent,  of  their  dry  weight  in 
each  case,  or  only  about  .33  of  an  inch. 


189.  Rate  of  Percolation  from  Soils. — The  percolation  of 
water  from  the  sandy  loam  and  from  the  clay  soil,  given 


160 


Physics  of  the  Soil. 


in  the  table  of  (160),  when  the  eight-foot  columns  were 
completely  full  of  water  at  the  start,  took  place  at  a  much 
slower  rate  than  from  the  sands,  as  indicated  in  (188),  the 
rates  being 


Sandy 
loam, 
inches. 

Clay 
loam 
inches. 

First  21  hours  

2.640 

First  23  hours  

1  953 

First  10  davs  following  the  above  

5.072 

2.111 

.905 

.493 

Total  in  about  21  days  

8.617 

4.562 

The  rates  in  these  cases  were  such  that  more  water  per- 
colated from  the  three  coarsest  sands  during  the  first  30 
minutes  than  from  the  clay  loam  in  as  many  days ;  and  yet 
the  loam  contained  at  the  start  the  largest  amount  of  water. 
It  is  clear  from  these  differences  in  the  rate  of  percolation 
why  the  sand  could  not  be  productive  under  ordinary  con- 
ditions of  rainfall,  no  matter  how  much  plant  food  it  might 
contain.  It  is  clear  also  that  fineness  or  closeness  of  tex- 
ture is  one  of  the  most  important  qualities  of  a  good  soil, 
for  without  this  the  water  drains  away  so  rapidly  that, 
with  the  ordinary  intervals  between  rains,  not  enough  could 
be  retained  for  the  needs  of  crops. 

190.  Percolation  Through  Dry  Soil. — When  soils  have  be- 
come relatively  dry,  as  happens  especially  during  the  mid- 
dle and  later  summer,  water  does  not  percolate  into  them 
as  readily  as  it  does  in  the  spring  when  the  pores  are  more 
nearly  filled.  When  the  volume  of  air  in  the  soil  is  large, 
and  when  the  films  of  water  surrounding  the  soil  grains  are 
very  thin,  the  flow  downward  past  the  air  is  very  slow. 
It  is  on  this  account,  in  part,  that  the  lighter  rains  are  less 
effective  in  midsummer  than  they  are  in  the  spring,  the 
water  being  retained  close  to  the  surface  where  it  is  quickly 
lost  by  evaporation. 


Capillary  Movements  of  Soil  Moisture.  161 


CAPILLARY   MOVEMENTS    OF   SOIL   MOISTURE. 

The  capillary  movements  of  soil  moisture  are  relatively 
slow,  when  compared  with  those  of  percolation,  and  are 
slower  in  dry  than  in  wet  soil. 

The  general  tendency  of  capillarity  is  to  bring  water  to 
the  surface  from  varying  depths,  but  its  movements  may 
occur  in  any  other  direction,  the  flow  being  always  from  a 
soil  where  the  water  films  are  relatively  thick  toward  those 
where  they  are  thinner,  or  from  the  wetter  toward  the 
dryer  soils. 

If  the  roots  of  plants  have  made  the  soil  dryer  in  their 
immediate  neighborhood  capillarity  may  carry  water  to 
them  from  below,  above  or  from  either  side.  When  heavy 
rains  follow  a  dry  spell  then  capillarity  will  assist  gravity 
in  carrying  the  water  more  deeply  into  the  ground ;  and 
when  water  is  applied  by  the  furrow  method  in  irrigation 
capillarity  carries  it  laterally  away  from  the  furrows. 

191.  The  Rise  of  Water   in   Capillary   Tubes. — When   a. 
clean  glass  tube  whose  bore  is  small  and  wet  is  held  verti- 
cally in  water  the  liquid  rises  to  a  certain  height  above  the 
level  outside,  the  amount  varying  with  the  diameter  of  tho 
tube,  as  given  in  the  table  below : 

In  a  tube  1.  inch  in  diameter  the  water  raises  .054  inches. 
In  a  tube  .1  inch  in  diameter  the  water  raises  .545  inches. 
In  a  tube  .01  inch  in  diameter  the  water  raises  5.456  inches. 
In  a  tube  .001  inch  in  diameter  the  water  raises  54.56  inches. 

That  is  to  say,  reducing  the  diameter  of  the  tube  one-half 
doubles  the  height  the  water  may  be  raised  by  capillarity, 
and  reducing  the  diameter  to  one-hundredth  enables  the 
water  to  rise  100  times  as  high.  The  results  in  the  table 
above  will  be  true  only  when  the  walls  of  the  tube  are  very 
clean,  the  water  pure  and  the  temperature  32°  F. 

192.  Cause  of  the  Variation  in  Height  to  Which  Water  Is 
Raised  in  Capillary  Tubes. — The  reason  for  the  differences 


1G2 


Physics  of  the  Soil. 


in  height  to  which  water  may  be  raised  in  capillary  tubes 
by  surface  tension  is  found  in  the  relation  existing  between 
the  volume  of  the  tube  and  its  internal  circumference  at 
the  level  of  the  water  surface.  Quinke  has  shown  that 
the  force  of  cohesion  is  exerted  over  a  distance  of  sWoo^ 
inch;  so  that  when  a  glass  tube  is  thrust  into  water  the 
molecules  in  the  surface  of  the  wall  just  above  the  water 
draw  upward  upon  the  rows  of  molecules  in  the  surface 
lying  nearest,  raising  them  above  the  naiural  water  level. 
But  as  the  edge  of  the  surface  film  is  raised  the  whole  water 
column  is  carried  upward  also  until  the  weight  lifted  above 
the  hydrostatic  level  is  equal  to  the  cohesive  attraction  be- 
tween the  glass  and  the  water. 

As  each  molecule  of  glass  has  a  fixed  power  to  pull,  the 
tube  of  large  diameter  will  be  able  to  lift  as  much  more 
water  than  the  small  one,  as  the  number  of  molecules  in 
its  circumference  is  greater.  But  the  circumferences  of 
tubes  increase  in  the  same  ratio  as  their  diameters,  and 
hence  a  tube  whose  diameter  is  .1  inch  will  lift  above  the 
water  level  10  times  as  much  wrater  as  the  one  .01  inch  in 
diameter.  But,  as  the  weight  of  water  lifted  increases  as 
the  squares  of  the  diameters  of  the  tubes,  the  first  tube 
will  only  lift  its  column  one-tenth  as  high  as  the  second 
tube,  for  then  its  load  becomes  10  times  as  great,  and  this 
is  the  limit  of  its  power,  as  expressed  in  the  table  below: 


Diameter  of  tube. 

Relative  area 
of  cross- 
sect  ion  of 
tube. 

Heieht  to 
which  water 
is  lifted. 

Relative 
amount   of 
water  lifted. 

1.0 
.1 
.01 
.001 

inch  

1,000,000  X      -05456  inches 
10,000  X       .5456    inches 
100  X    5.456      inches 
1  X  54.560      inches 

—   54,.  VO  00 

inch  

=     5.45fi.OO 
—         546  00 

—         5tt5  50 

The  actual  amount  of  water  lifted  by  the  surface  film 
stretched  across  the  tube  and  carried  upward  by  the 
pull  of  the  glass  molecules  just  above  its  edge  is  as  fol- 
lows , 


Capillary  Movements  of  Soil  Moisture.          1G3 

In  the  1.0      inch  tube 01285        cubic  inch. 

In  the     .1      inch  tube 0012S5      cubic  inch. 

In  the     .01    inch  tube 0001285    cubic  in<;h. 

In  the    .001  inch  tube 00001285  cubic  inch. 

193.  Capillary  Rise  of  Water  in  Soils. — The  spaces  left  be- 
tween the  soil  grains  form  more  or  less  triangular  capillary 
tubes  whose  cross-section,  formed  by  four  spherical  grains, 
placed  as  closely  together  as  possible,  is  represented  at  the 
left  in  Fig.  54;  and  these  tubes  extend  in  all  directions 
through  a  soil. 

The  effective  diameters  of  these  capillary  tubes  are 
somewhat  nearly  proportional  to  the  diameters  of  the  soil 
grains  so  that  for  soils  with  spherical  grains  having  the 
closest  pcickiug,  doubling  the  diameters  of  the  grains  would 
also  double  the  effective  diameters  of  the  capillary  tubes 
through  which  the  water  must  be  moved. 


FIG.  54.— Showing  the  shape  of  cross-sections  of  the  pore  space  between 

soil  grains. 

Tli3  area  of  cross  section  of  the  two  capillary  pores 
shown  in  Fig.  54  is  equal  to  the  area  of  the  rhombus  con- 
necting the  centers  of  the  four  grains  minus  the  area  of  a 
circle  having  the  diameter  of  the  soil  grains,  so  that  divid- 
ing this  area  by  two  gives  the  area  of  the  section  of  the 
pore. 

Where  the  pore  has  the  smallest  section  its  area  is  given 
by  the  equation 


Area  =  (v3  —  -^J  X  r8  =  .1613  r8 
where  r  is  the  radius  of  the  soil  grain, 


164  Physics  of  the  Soil. 

.The  capillary  pores  in  an  ideal  soil  do  not  have  a  uni- 
form diameter  but  are  shaped  like  the  cast  shown  in  Fig. 


FIG.    55.— Showing   a    cast   of  the   pore   space   between   spherical    grains, 
much   enlarged. 

55,  largest  at  one  place  and  decreasing  in  either  direc- 
tion to  the  area  given  by  the  equation  above.     The  mean 
area  of  the  section  of  the  pore,  is  given  by  Slichter,*  as 
mean  area  of  section  of  pore  =  0.2118  r2 

which  would  make  the  largest  or  effective  cross  section 
of  the  capillary  pore  not  far  from 

(.2118  X  2)  —  .1613  =  .2623  r2 

From  this  the  effective  diameter  of  the  capillary  tubes 
may  be  found,  using  the  formula 

D  =  2  -/-2623r8 

where    r  is  the  radius  of  the  soil  grain 

and     D  is  the  diameter  of  the  capillary  pore. 

*  Theoretical  Investigation  of  the  Motion  of  Ground  Waters,  19th 
annual  report  of  the  Geological  Survey,  part  II,  p.  316, 


Capillary  Movements  of  Soil  Moisture.  165 

On  this  basis  spherical  soil  grains  of  one  size  and  the 
closest  packing,  having  diameters  of 

m.  m.        m.  m.        m.  m.        ru.  m.        m.  m. 
1.  .5  .1  .05  .01 

would  form  capillary  tubes  whose  largest  cross  sections 
are  nearly  equivalent  in  area  to  circles  having  diameters  of 

m.  m.    m.  m.    m.  m.    m.  m.    m.  m. 
.289    .1445    .0289    .01445   .00289 

Did  such  soil  grains  have  the  attractive  power  of  glass 
for  water  and  were  their  triangular  pores  capable  of  rais- 
ing water  to  the  height  of  circular  tubes  of  equivalent 
cross  sections  they  should  be  able  to  lift  water  at  32°  F. 
to  very  nearly  the  height  of 

.4ft.     .8ft.        4ft.     8  ft.  and  40  ft.  respectively. 

194.  Observed  Height  of  Capillary  Rise  of  Soil  Moisture — 
To  measure  the  rise  of  water  by  capillarity  in  ordinary 
soils  four  cylinders,  10  feet  long  and  .04611  sq.  ft,  in  sec- 
tion, were  filled,  two  with  a  sandy  loam  and  two  with 
a  clay  loam,  the  first  containing  18.88  per  cent.,  and  the 
second  32.63  per  cent,  of  water  uniformly  distributed 
throughout  the  columns.  On  one  of  each  set  of  tubes  a 
soil  mulch  was  developed  3  inches  deep,  when  they  were 
all  placed  in  front  of  a  ventilator  where  a  current  of  air 
was  maintained  across  their  tops  during  314  days.  At 
the  end  of  this  time  the  tubes  were  cut  into  6-inch  sec- 
tions and  the  water  content  of  the  soil  determined,  with 
the  results  given  in  the  table  which  follows: 

It  is  clear  from  this  table  that  there  has  been  an  up- 
ward movement  of  water  and  loss  through  the  surface 
even  from  the  bottom  layers  of  soil  in  the  case  -of  the 
medium  clay,  and  probably  also  from  the  sandy  loam. 
This  follows  from  the  fact  that  the  clay  soil  contained, 
when  put  into  the  cylinders,  32.63  per  cent.,  whereas  the 
lower  six  inches  is  1.38  per  cent,  drier  in  the  mulched  cyl- 
inder and  3.17  per  cent,  drier  in  the  cylinder  not  mulched. 


1G6 


Physics  of  the  Soil. 


Table  showing  the  loss  of  water  by  surface  evaporation  from 
columns  of  soil  10  feet  long,  mulched  and  not  mulched. 


SAND?  LOAM. 

CLAY  SOIL. 

Mulched 
3  inches. 

Not 
mulched. 

Mulched 
3  inches. 

Not 
mulched. 

Per  cent. 

8.33 
12  97 
14.59 
15.25 
15.55 
15.89 
16.22 
16.29 
16.58 
17.07 
17.05 
17.26 
17.56 
17.73 
17.94 
17.96 
18.25 
18.67 
18.53 
19.21 

Per  cent. 

7.41 
14.48 
14.70 
14.96 
15.53 
16.17 
16.33 
16.  33 
16.10 
16.76 
17.31 
17.43 
17.79 
17  88 
17.85 
17.67 
18.05 
18.09 
18.63 
19.95 

Per  cent. 

17  66 
24.59 
26.58 
26.95 
27.45 
27.92 
27.94 
28.24 
28.46 
28.47 
28.87 
28.70 
29.24 
29.28 
29.  35 
29.79 
30.32 
31.15 
30.47 
31.25 

Per  cent 

7.79 
18  30 
21  46 
26  26 
26.  S9 
27  .  16 
27  61 
27.64 
27.28 
28.23 
27.79 
28.05 
28.93 
28.31 
28.32 
28.80 
29.14 
29.16 
29.33 
29.46 

6  inches  to    12  inches  

12  inches  to  18  inches  

24  inches  to   30  inches  

36  inches  to   42  inches  

48  inches  to    54  inches  
54  inches  to   60  inches  

60  inches  to  86  inches  

66  inches  to    72  inches  

72  inches  to   78  inches  

78  inches  to   84  inches  

90  inches  to   96  inches...   

102  inches  to  108  inches  

108  inches  to  114  inches  

Hi  inches  to  120  inches  .  .. 

In  the  case  of  the  sandy  loam  the  lower  six  inches  in  each 
case  is  wetter  than  when  it  went  in,  showing  that  at  first 
percolation  downward  had  taken  place,  and  as  this  soil 
when  allowed  to  drain  freely  only  retained  19.44  per  cent. 
of  water  at  a  depth  of  36-42  inches,  it  is  quite  probable 
that  at  some  time  the  lower  soil  10  feet  below  the  sur- 
face may  have  been  wetter  than  found  at  the  end  of  the 
trials,  and  if  this  is  true  then  even  the  sandy  loam  has 
lost  water  upward  from  a  depth  of  ten  feet  below  the  sur- 
face. 

It  is  quite  certain  that  a  drying  of  these  soils  has  taken 
place  through  a  depth  of  ten  feet,  and  hence  that  moisture 
ten  feet  below  the  surface  of  the  ground  may  become 
available  for  vegetation  purposes  at  or  near  the  surface. 

The  effective  diameter  of  the  soil  grains  in  these  two 
cases  was  found  to  be,  for  the  sandy  loam,  about  .01635 
m.  m.,  and  for  the  medium  clay  loam,  .01254  m.  m. ;  this 
would  indicate  that  there  might  be  a  capillary  rise  of  23.6 
and  30.8  feet  respectively. 


Capillary  Movements  of  Soil  Moisture.          167 


195.  Capillary  Rise  of  Water  in  Sand. — In  the  case  of  a 
sorted  sand  with  grains  .4743  m.  m.  in  diameter,  when 
saturated  with  water  in  an  apparatus  represented  in  Fig. 
56,  it  was  found  that  water  was  raised  through  a  col- 
umn 6.75  inches  above  the  level  of  water  in  the  reservoir 
at  the  rate  of  44.09  inches  of  water  on  the  level  per  24 
hours,  but  that  when  the  column  was  made  11.75  inches 
long  no  water  was  raised  to  the  surface. 


ill 


FIG.  56.— Apparatus  for  measuring  the  maximum  rate  and  height  of 
capillary  rise  of  water  in  sands.  A,  evaporating  reservoir;  B,  water 
reservoir;  C,  rubber  tube. 


From  the  formula  in  (193)  a  glass  sand  with  grains  the 
size  of  this  one  should  be  able  to  lift  water  by  capillarity 
to  a  height  of  10.11  inches  and,  since  the  quartz  sand  used 
did  lift  water  at  the  rate  of  44.09  inches  in  depth  in  24 
hours  through  a  height  of  6.75  inches,  and  failed  to  lift 
any  water  to  a  height  of  11.75  inches,  it  is  clear  that  its 
maximum  limit  must  lie  very  close  to  that  computed  for 
the  glass  sand. 


168 


Physics  of  the  Soil. 


196.  Rate  of  Capillary  Rise  of  Water  in  Wet  Soil. — There 
is  yet  no  very  satisfactory  data  as  to  just  how  rapidly  wa- 
ter may  be  moved  by  capillarity  through  wet  soils.  It  is 
probable  that  the  case  cited  in  (195)  represents  about  the 
maximum  rate  in  that  coarse  quartz  sand,  through  that 
height,  namely,  44.09  inches  in  depth  per  24  hours.  This 
is  an  enormous  quantity  of  water  to  be  raised  by  capil- 
larity and  was  rendered  possible  only  by  expanding  the 
column  of  sand  at  the  top,  as  shown  in  the  figure,  so  as  to 
increase  the  rate  of  evaporation  until  it  exceeded  the  abil- 
ity of  capillarity  to  bring  the  water  to  the  surface. 

Experiments  have  shown  that  with  a  strong  current  of 
air  passing  across  the  wet  surface  of  the  soil,  water  was 
lifted  by  capillarity  in  a  square  foot  of  soil,  through  the 
different  distances  and  at  the  rates  given  in  the  table  be- 
low: 


1  foot. 

2  feet. 

' 

3  feet. 

4  feet. 

Fine  quartz  sand  

Ibs.  per  day 

2.37 

ibs.  per  day. 
2.07 

Ibs.  per  day. 
1  .  23 

Ibs.  per  day. 
.91 

2  05 

1.G2 

1.00 

.00 

It  is  quite  certain  that  these  figures  do  not  represent  the 
maximum  rate  of  capillary  rise  through  these  soils;  be- 
cause, as  the  surface  of  the  soil  had  no  greater  area  than 
the  section  of  the  soil  column,  the  rate  of  rise  could  not 
exceed  the  rate  of  evaporation. 

197.  Rate  cf  Capillary  Movement  of  Water  in  Dry  Soil — 
The  movement  of  water  through  a  thoroughly  dry  soil,  by 
capillarity,  is  not  as  rapid  as  it  is  through  the  same  soil 
when  wet;  the  case  being  analogous  to  the  much  slower 
absorption  of  water  by  a  dry  cloth  or  sponge  than  by  a 
similar  one  when  damp. 

In  the  table  which  follows  is  given  the  rate  at  which 
water  entered  5  cvlinders  of  water-free  soil,  6  inches  in 


Capillary  Movements  of  Soil  Moisture.  169 


diameter  and  12  inches  long,  standing  in  one  inch  of  wa- 
ter and  possessing  the  undisturbed  field  texture.  The 
cylinders  stood  in  a  saturated  atmosphere  and  the  amount 
of  water  absorbed  was  determined  by  weighing  every  third 
day,  the  samples  being  the  same  ones  used  in  (158)  and 
(159). 

Table  showing  the  mean  daily  absorption  of  capillary  water 
by  undisturbed  field  soil.  Cylinders  6  inches  in  diameter, 
12  inches  long,  standing  11  inches  out  of  water. 


POUNDS  PEE  CUBIC  FOOT. 

First 
foot. 

Second 
foot. 

Third 
foot. 

Fourth 
foot. 

Fifth 
foot. 

Water  absorbed  dur  ng  1st   3  days  
Water  absorbed  rlui  tig  2nd  3  days  

12.50 
2.57 
1.74 
1  33 
.96 
.44 
.It 
.07 

19.73 

Per  ct. 
32  2 

28.28 

3.92 

12.42 
2  18 
1.02 

.79 
.59 
.46 
.32 
.25 

18  03 

Per  ct. 

23.8 
20.43 

3.37 

9  61 
2  33 
1.56 
1.28 
1.16 
1.00 
.69 
.48 

18.32 

Per  ct. 
24.5 
20  39 

4.11 

13  50 
3.f'8 
1.71 
.51 
.-3 
17 
.10 
.03 

19  83 

Per  ct. 
22  6 
21.30 

1.30 

10.73 
2  9:i 
2.15 
.61 
.16 
.Oo 
.01 
.02 

16.67 

Per  ct. 
17  5 
15.72 

1.78 

Water  absorbed  dur  iisf  4th  3  days  

Water  absorbed  dur  ng  5th  3  days.,  
Water  absorbed  dur  ng  tith  3  days  

Water  absorbed  dur  ng  7th  3  days  

Water  absorbed  dur  ng  Sth  3  days  

Water  absorbed  during  24  days  

Complete  saturation  

Degree  of  saturation  attained  

Difference  

±'rom  this  table  it  is  seen  that  the  amount  of  water 
absorbed  during  the  first  three  days,  was  only  at  the  mean 
daily  rate  of  4.16,  4.13,  3.20,  4.5  and  3.58  Ibs.  respective- 
ly; after  the  first  period  the  rate  of  rise  was  much  less 
rapid  and  did  not  equal  the  rate  at  which  an  almost  iden- 
tical soil  (196)  raised  water  through  4  feet  as  measured 
by  the  daily  evaporation ;  and  yet  the  daily  rise  of  water 
of  .91  and  .90  Ibs.  per  sq.  ft,  would  have  been  greater 
had  the  evaporation  only  been  more  rapid.  In  the  case 
of  the  sand  of  (195)  the  water  was  lifted  by  capillarity  at 
the  enormous  rate  of  228.6  Ibs.  per  sq.  ft.  in  24  hours 
while  the  sandy  loam  of  (194),  placed  under  the  conditions 
of  (195),  using  the  same  piece  of  apparatus,  lifted  water 
at  the  rate  of  26.62  Ibs.  per  sq.  ft.  in  the  same  24  hours. 


170  Physics  of  the  Soil. 

In  the  case  of  the  6-inch  cylinders  of  soil  above,  with 
their  tope  only  11  inches  out  of  water,  the  length  of  time 
required  for  the  surface  of  the  soil  to  begin,  to  appear 
damp  was 

2  days  for  the  fine  sand  or  5th  foot. 

6  days  for  the  sand  and  clay  or  4th  foot. 

6  days  for  the  clay  loam  or  1st  foot. 
18  days  for  the  reddish  clay  or  3rd  foot. 
22  days  for  the  reddish  clay  or  2nd  foot 

It  is  clear  from  the  data  presented  that  the  rate  of  cap- 
illary movement  of  soil  moisture  is  greatly  influenced  by 
the  water  content  of  the  soil. 

198.  Capillarity  Is  Stronger  in  Wet  than  in  Dry  Soils. — It 
follows  from  (196)  and  (197)  that  capillary  action  in  a 
given    soil    is    stronger  when  the  soil  contains  a  certain 
amount  of  moisture  than  it  is  when  that  amount  is  much 
reduced.      When  soils  have  their  water  content  so  much 
reduced  that  they  begin  to  look  dry,  and  especially  after 
they  become    air-dry,  they   act  as    effective  mulches    and 
water  will  neither  rise  through  them  so  rapidly  nor  so  high 
the  dryer  they  become,  and  if,  under  these  conditions,  a 
light  shower  should  fall  it  might  have  the  effect  of  leaving 
the  surface  soil  with  a  greater  increase  of  moisture  than  is 
represented  by  the  rain  which  fell. 

199.  Kain  May  Cause  a  Capillary  Kise  of  the  Deeper  Soil 
Moisture. — It  was  observed  in  1889,  when  determining  the 
water  content  of  soils  at  different,  depths  in  the  field,  just 
before  and  immediately  after  rains,  that  frequently  the 
lower  soil  showed  a  smaller  amount  of  moisture  than  it 
had  before  the  rain,  while  the  surface  layers  had  gained 
in  water  more  than  that  represented  by  the  rainfall.     It 
was  later  shown  that,  by  applying  a  known  amount  of 
water  to  a  section  of  a  field,  the  lower  soil  became  dryer 
while  the  surface  layers  had  gained  more  water  than  was 
added,  as  shown  in  the  table. 


Capillary  Movements  of  Soil  Moisture.  171 

Table  showing  the  translocation  of  soil  moisture  due  to  welting 
the  surface. 


DEPTH. 

PERCENT.  OF  WATER. 

DIFFERENCE. 

Befr.re 
wetting. 

After 
wetting. 

In  per 
cent 

In  pounds 
per  cub.  ft. 

0-6  inches  

14. 
15  14 

16.23 
17.70 
16.76 
15.51 

22.23 
15  71 
15.75 
16  92 
14  41 
15.21 

+  8.23 
+    .57 
-     .48 
-     .78 
—  2.35 
—     .30 

+2.873 
-f  .199 
-  .213 
—  .347 
—I.I  '32 
—  .132 

6  inches  to  12  inches  

18  inches  to  24  inches  

30  inches  to  36  inches  

The  amount  of  water  applied  to  the  surface  in  this  ex- 
periment was  2  Ibs.  per  sq.  ft.  but  when  samples  of  soil 
were  taken  26  hours  later  there  had  been  an  increase  of 
3.072  Ibs.  in  the  surface  foot  and  a  loss  of  1.724-  Ibs.  from 
the  second  and  third  feet.  Observation  showed  that  a  tray 
of  soil,  on  a  pair  of  scales  at  the  place,  lost,  by  evapora- 
tion during  the  same  time,  .428  Ibs.  per  sq.  ft.  ;  and,  as-1 
suming  that  the  field  soil  lost  water  at  the  same  rate,  makes 
the  water  to  be  accounted  for 

3.072+  .428  =  3.  5  Ibs., 

while  the  total  loss  from  the  lower  two  feet  plus  the  water 
added  was 

.721  =  3.7241b3. 


an  amount  as  nearly  equal  to  the  3.5  Ibs.  as  could  be  ex- 
pected. 

In  another  trial,  adding  1.33  Ibs.  of  water  to  the  sur- 
face produced  the  gain,  by  translocation  upward  into  the 
upper  four  feet,  shown  in  the  next  table. 


172 


Physics  of  the  Soil. 


DEPTH. 

WATEB  CONTENT  OF  THE  SOIL. 

Before 
•wetting. 

After 
•wettiug. 

Change. 

Pounds  per 
cu.  ft. 
11.78 
15  79 
11  7:! 
14.02 

Pounds  per 
cu.  ft. 
14  06 
17  52 
15.53 
15.40 

Pounds  per 
cu.  ft. 
2.28 
1.73 
.85 
1.37 

Third  foot        

Fourth  foot  

6.23 

The  interval  during  this  experiment  was  one  of  very 
little  evaporation  and  the  adjacent  untreated  ground  gained 
1.21  Ibs.  per  sq.  ft.  in  the  same  depth.  This  amount  and 
the  water  added  deducted  from  the  gain  in  the  treated  area 
leaves  the  translocation 

6.23— (1.21+  1.33)  =  3. 69  Ibs.  per  sq.  ft. 

200.  Farmyard  Manure  May  Strengthen  Capillary  Rise  of 
Soil  Moisture. — When  a  soil  is  treated  with  farmyard  ma- 
nure which  has  become  well  incorporated  with  it,  it  has 
the  effect  of  causing  a  stronger  rise  of  the  deeper  soil 
moisture  into  the  surface  three  feet,  where  it  is  most 
needed  in  the  production  of  crops.  The  table  which  fol- 
lows shows  the  mean  results  of  experiments  aiming  to 
measure  this  effect  during  three  years. 

Table  showing  effect  of  farmyard  manure  in  strengthening  the 
capillary  rise  of  soil  moisture. 


1st  foot. 

2nd  foot. 

3rd  foor. 

4th  foot. 

5th  foot. 

6th  foot. 

Manured  

Per  cent, 
of  watar. 

ly  88 

18.79 

Per  cent, 
of  water. 
19.79 
19.33 

Per  cent, 
of  water. 

18.88 
18.60 

Per  cent, 
of  water. 
17.29 
17  32 

Per  cent, 
of  watpr. 
14.35 
14.63 

Per  cent, 
of  water. 
16.  9« 
17.13 

Not  manured  

Difference  

+1.09 

+  .46 

+  28 

—.03 

-.28 

-.15 

It  is  seen  here  that  the  surface  three  feet  have  in  some 
way  been  maintained  more  moist,  and  apparently  by  the 
manure,  at  the  expense  of  moisture  from  below. 


Capillary  Movements  of  Soil  Moisture. 


201.  Heavy  Soil  Mulches  May  Strengthen  the  Capillary 
Rise  of  Soil  Moisture. — Since  capillary  action  is  not  as 
strong  in  a  dry  as  in  a  well  moistened  soil  it  should  be 
anticipated  that  any  condition  which  would  maintain  a 
fair  degree  of  saturation  in  the  surface  one  to  three  feet 
of  soil  would  permit  it  to  bring  up  from  below,  for  the 
use  of  crops,  a  larger  supply  of  capillary  water. 

On  three  different  kinds  of  soil,  where  the  ground  had 
been  cultivated  during  the  season  in  alternate  groups  of 
four  rows  3  inches  deep  and  1.5  inches  deep,  the  distribu- 
tion of  moisture,  on  July  16,  was  found  to  be  as  follows: 

Table  showing  the  effect  of  mulches  in  strengthening  the  capil- 
lary rise  of  soil  moisture. 


1st  foot. 

2nd  foot. 

3rd  foot. 

4th  foot. 

Field  No.  1  cultivated  3 
Field  No.  1  cultivated  1 

Difference  

inches  deep 
5  inches  deep  — 

Perct.  of 
water. 
11.30 
9.92 

Per  ct.  of 
water. 
15.57 
15.43 

Per  ct.  of 
watfr. 
10  54 
11.56 

Per  ct.  of 
water. 
11.37 
13.99 

1.88 

.14 

—1.02 

-1.62 

Field  No.  2  cultivated  3 
Field  No.  2  cultivated  1 

Difference  

inches  deep  
5  inches  deep  — 

13  96 
12.98 

22.74 
20.44 

2339 
24  02 

19.47 
21.31 

.93 

2.30 

-.03 

-1.87 

Field  No.  3  cultivated  3 
Field  No.  3  cultivated  1 

Difference  

inches  deep  — 
5  inches  deep  — 

11.65 
10.65 

17.47 
16.85 

16.44 
17.81 

13.03 
13.32 

1.00 

.62 

-1.37 

-.29 

This  table  indicates  that  the  3-inch  mulch,  by  main- 
taining the  surface  soil  more  moist,  enabled  capillarity  to 
bring  up  from  below  a  larger  supply  of  water;  that  is, 
the  maintaining  of  a  relatively  high  per  cent,  of  moisture 
in  the  upper  two  feet  of  soil  makes  it  possible,  through 
capillarity,  for  crops  to  utilize  a  larger  amount  of  the  soil 
moisture  which  is  stored  in  the  deeper  layers.  This 
view  is  confirmed  by  the  fact  that,  in  the  fields  of  the  ta- 
ble above,  the  largest  yields  of  corn  were  in  all  cases  taken 
from  the  ground  cultivated  3  inches  deep,  where  the  up- 


m 


Pliysics  of  the  Soil. 


per  two  feet  of  soil  contained,  in  spite  of  the  larger  crop, 
much  more  moisture,  but  at  the  expense  of  that  deeper  in 
the  ground,  as  shown  by  the  fact  that  in  every  case  these 
soils  were  dryest  in  the  3d  and  4th  feet 

202.  Firming  the  Soil  May  Strengthen  the  Capillary  Rise 
of  Soil  Moisture. — When  soils  have  been  rendered  open  and 
loose  by  plowing  or  other  deep  stirring  the  first  effect  is 
to  permit  the  loose  and  open  soil  to  become  dry,  because 
this  soil  is  less  perfectly  in  contact  with  that  below.  If, 
after  such  soil  has  become  dry,  it  is  firmed  again  the  moist- 
ure films  will  then  increase  in  thickness  over  the  surface 
of  the  soil  grains  and,  as  a  result  of  this,  moisture  will 
be  raised  from  depths  as  great  as  four  feet  to  saturate  the 
firmed  dryer  soil.  In  the  table  below  are  shown  tho 
changes  which  occurred  in  the  deeper  and  superficial  soil 
layers  as  the  result  of  rolling. 

Table  showing  how  rolling  may  strengthen  the  capillary  rise 
of  soil  moisture. 


Depth  of  sample. 

No.  of 

trials. 

Rolled 
ground. 

Unrolled 
ground. 

Change 
produced. 

Surface  2  to  18  inches  

62 

Per  cent. 
of  water. 
15.85 

Per  cent, 
of  water. 
15  t>4 

Per  cent, 
of  water. 

+  .21 

Surface  24  inches  

61 

19.49 

19.85 

—.36 

Surtace  36  to  54  inches  ..     -  

24 

18  72 

19.43 

—.71 

From  this  table  it  is  seen  that  the  first  effect  of  rolling 
is  to  increase  the  amount  of  moisture  in  the  upper  18 
inches  of  soil,  but  that  when  samples  are  taken  deeper  than 
18  inches  the  total  amount  in  the  soil  is  decreased.  In 
other  words,  the  first  effect  is  to  concentrate  the  deeper 
soil  moisture  toward  the  surface. 

If,  however,  the  soil  is  left  firmed  very  long  then  the 
whole  column,  to  the  surface,  becomes  dryer,  until  it  has 
lost  so  much  moisture  that  it  beg-ins  to  act  as  a  mulch. 


Thermal  Movements  of  Soil  Moisture.  175 


THERMAL  MOVEMENTS  OF  SOIL  MOISTURE. 

Besides  the  gravitational  and  capillary  movements  of 
soil  moisture  there  are  others  due  to  the  molecular  vibra- 
tions set  up  in  the  soil-air  and  water  by  the  absorbed  solar 
energy. 

203.  Hygroscopic  Soil  Moisture — It  is  seldom  if  ever  true 
that  any  solid  surface,  even  when  in  the  dryest  air,  can 
be  found  which  is  not  invested  with  a  film  of  moist uro 
of  greater  or  less  thickness.  It  is  also  true  that  even  when 
all  moisture  has  been  driven  from  the  surface  of  a  solid 
by  drying  at  the  high  heat  of  200°  C.,  the  same  body  will 
again  become  coated  with  moisture  when  exposed  to  a 
moisture-bearing  atmosphere.  Water  thus  collected  on 
the  surface  of  solids  is  called  hygroscopic  moisture. 

204.  The  Movements  of  Hygroscopic  Moisture. — It  will  be 
seen  that  the  movements  of  hygroscopic  moisture  are  the 
same  as  those  of  evaporation.  The  same  molecular  at- 
traction which  causes  the  capillary  rise  of  water  in  a  glass 
tube  tends  to  collect  the  water  molecules,  which  may  be 
moving  about  in  the  air,  upon  solid  surfaces.  So  when 
a  dry  soil  is  exposed  to  a  damp  atmosphere  some  of  the 
moving  water  molecules  are  brought  in  contact  with,  and 
retained  by,  the  surfaces  of  the  soil  grains.  The  moisture 
will  go  on  accumulating  upon  the  soil  grains  until  the  rate 
of  evaporation  from  them  equals  the  rate  of  condensation. 
Since  the  water  molecules  are  attracted  to  the  soil  grains 
more  strongly  than  they  are  attracted  to  one  another  the 
water  in  immediate  contact  with  the  soil  grains  cannot 
evaporate  as  readily  as  that  which  is  further  removed  when 
the  water  films  are  thick,  as  they  are  in  a  well  saturated  soil. 

Neither  can  the  innermost  layers  of  molecules  adhering 
to  the  soil  grains  escape  to  enter  the  root  hairs  of  plants  by 
osmotic  pressure  as  readily  as  those  from  the  layers  farther 
removed,  and  hence  there  must  always  be  a  certain  quan- 
tity of  water  upon  the  surfaces  of  soil  grains  which  neither 


176  Physics  of  the  Soil. 

evaporates  readily  nor  becomes  easily  available  to  plants, 
and  this  may  be  regarded  as  the  hygroscopic  moisture. 

205.  Relation  of  the  Diameter  of  Soil  Grains  to  the 
Hygroscopic  Moisture. — It  was  shown  in  (163)  that  with 
the  same  thickness  of  water  surrounding  the  soil  grains 
the  per  cent,  of  water  was  necessarily  much  higher 
in  the  soils  having  the  smallest  soil  grains.  In  (192)  is 
given  Quincke's  observation  of  the  distance  across  which 
the  force  of  cohesion  is  sensible,  or  CT^OTT  inch.  Since 
this  attraction  of  the  soil  for  water  is  stronger  than  that 
of  the  water  for  the  water  it  appears  likely  that  a  layer 
of  water  surrounding  the  soil  grains,  at  least  as  thick  as 
this,  would  not  be  as  free  to  evaporate  or  to  otherwise  move 
about  as  that  much  farther  removed  from  this  cohesive 
attraction,  and  if  so  it  is  important  to  know  what  per 
cents  of  soil  moisture  a  water-film  of  such  a  thickness  would 
represent.  This  may  be  computed  for  spherical  soil 
grains  with  the  formula 

jf  (d  +  2t)3         n  d8 
Per  cent,  of  water  =  , 


it  ds  sp.  gr. 

6 
where    d  =  diameter  of  soil  grain  in  c.  m. 

t  =  thickness  of  water  film, 
sp.  gr.  —  the  specific  gravity  of  the  soil. 

Taking  a  very  fine  soil  having  grains  with  a  diameter 
of  .00508  m.  m.  and  a  coarse  one  with  a  diameter  of  .1 
m.  m.,  a  film  of  moisture  on  each,  having  the  thickness  of 
the  range  of  sensible  cohesive  attraction,  as  given  by 
Quincke,  would  make  the  per  cent,  for  the  finest  soil  2.31 
but  for  the  coarse  soil  only  .1153.  No  crop  can  survive  in 
soils  as  dry  as  these;  and  air-dry  soils  whose  grains  range 
between  those  given  will  generally  contain  more  than  these 
amounts  of  moisture.  It  follows  from  these  considera- 
tions, therefore,  that  what  has  been  regarded  as  the  hygro- 
scopic moisture  is  more  than  that  held  within  the  range 


Thermal  Movements  of  Soil  Moisture.  177 

of  sensible  cohesive  attraction.  It  appears  clear  also  that 
no  hard  and  fast  line  can  be  drawn  between  capillary  and 
hygroscopic  moisture,  nor  indeed  between  cither  of  these 
and  the  gravitational  water;  each  must  shade  by  insensi- 
ble decrees  into  the  other. 


to' 


206.  The  Amount  of  Moisture  a  Soil  May  Absorb  from  the 
Air. — The  amount  of  so-called  hygroscopic  moisture  a  given 
soil  may  absorb  from  the  air  depends  primarily  upon  ihr 
relative  temperature  of  the  soil  and  of  the  air  and  its  dej 
gree  of  saturation.     If  the  temperature  of  a  soil  could  be 
maintained  continually  below  that  of  a  saturated  atmos- 
phere above,  it  would  in  time  become  so  fully  charged  with 
water  as  to  result  not  only  in  capillary  saturation  but  in 
percolation  as  well ;  and  it  frequently    occurs    on    clear 
nights  in  summer,  when  dews  are  heavy,  that  a  thick,  loose, 
dry  dust  blanket  will  cool  down  so  much  that  moisture 
condenses  upon  it  in  sufficient  quantity  to  make  it  appear 
damp.     Indeed  dew,  wherever  it  forms,  is  a  demonstra- 
tion of  the  truth  of  the  statement  made;  when  it  evapo- 
rates with  the  rising  of  the  sun  the  loss  of  moisture  from 
the  blades  of  grass  may  carry  the  amount  all  the  way  from 
the  drops,  too  heavy  to  be  retained  upon  the  blades,  through 
the  thick  adhering  films,  to  those  which  become  invisible 
and  are  called  hygroscopic. 

207.  Observed  Absorption  of  Moisture  from  the  Air. — The 
rate  and  amount  of  moisture  which  may  be  absorbed  from 
the  air  is  influenced  by  many  factors.     Hilgard  has  studied 
the  rate  and  amount  of  absorption  of  moisture  by  soils  when 
spread  out  in  layers* about  1  m.  m.  thick  in  a  fully  saturated 
and  a  half  saturated  atmosphere,  maintained  at  a  uniform 
temperature.     He  finds  that  fully  7  hours  are  required 
for  an  equilibrium  to  be  reached  in  so  thin  a  layer.     In 
the  table  which  follows  are  given  some  of  his  observations. 


178 


Physics  of  the  Soil. 


Table  showing  the  absorptive  power  of  soils  spread  out  in  thin 

layers. 


SATURATED  ATMOSPHERE 

HALF  SATURATED 
ATMOSPHERE. 

KIND  OF  SOIL. 

Temp. 
Far." 

Time, 
hrs. 

Per  cent, 
of  water 
absorbed. 

Temp. 
Far." 

Time, 
hrs. 

Per  cont. 
of   water 
absorbed 

[     58 

19 

11.745 

57 

43 

6  547 

59 

19 

11.8^6 

Dark  alluvial  loam,  Putah 
Valley,  Solano  county... 

61 
•!      72 

77 

18 
7 
7 

11.40H 
12.  OH 
12.2*J 

70 

77 

7 
7.5 

6.424 
6.305 

88 

7 

13.141 

88 

7 

6.H56 

I  100 

6 

13.481 

100 

6 

6.209 

r  55 

19 

7.144 

61 

18 

4.008 

Black  adobe  soil,  Univer- 
sity   grounds,    Alameda 
county  

57 
!     70 
|     80.5 
82.5 

19 
7 
17 
7.5 

7.880 
7.696 
8.681 
8.948 

61 

80 
83 
89.5 

7  5 
6 

7.5 
7.5 

4  122 

4.024 
3  92S 
3.910 

I  100 

7 

9.569 

100 

7 

3.  885 

r   ei 

18 

2.133 

59 

18 

0  987 

Calcareous  silt  soil,  Fresno 

J     79 

6 

2.983 

79 

6 

O.i-59 

county  

84 

7 

3.396 

84 

7 

0  818 

I     95 

6 

4.211 

95 

6 

0.821 

It  will  be  seen  that  in  the  saturated  atmosphere  the 
largest  amount  of  moisture  was  absorbed  at  the  highest 
temperature,  while  the  reverse  was  true  in  the  half  sat- 
urated atmosphere.  Under  the  high  temperature  the  rate 
of  molecular  movement  is  so  rapid  that  the  rate  at  which 
the  water  from  the  air  falls  upon  and  enters  the  soil  is  so 
much  increased  that  more  water  must  have  accumulated 
in  the  soil  before  the  number  of  molecules  which  can 
leave  its  surface  in  a  unit  of  time  equals  that  which  falls 
upon  it.  In  the  dryer  atmosphere,- on  the  other  hand, 
where  there  are  less  molecules  to  fall  upon  the  soil  and 
increase  its  amount,  the  higher  temperature  favors  the 
rapid  escape  as  much  as  when  the  saturation  was  high 
and,  since  less  water  is  condensing,  a  lower  per  cent,  is 
finally  present  when  an  equilibrium  of  interchange  has 
been  reached. 


Thermal  Movements  of  Soil  Moisture.  179 

208.  Internal  Evaporation  of  Soil  Moisture. — It  is  likely 
that  under  certain  conditions  the  thermal  movements  of 
soil  moisture  may  be  considerable  and  perhaps  of  sufficient 
importance  to  materially  influence  vegetation,  directly  or 
indirectly.  When  the  per  cent,  of  unoccupied  pore  space 
in  a  soil  has  been  materially  increased  by  the  loss  of  wa- 
ter and  when  the  moisture  films  have  become  so  thin  that 
capillarity  is  much  enfeebled  it  is  possible  that  internal 
evaporation  of  soil  moisture  may  result  in  a  considerable 
change  of  its  position.  If,  for  example,  when  the  soil  has 
become  quite  dry,  to  considerable  depths,  the  surface  six 
inches  should  become  cooler  than  that  below,  the  tendency 
to  continual  diffusion  of  water  vapor  under  the  impulse 
of  heat  would  produce  more  internal  evaporation  of  moist- 
ure where  the  soil  is  warmest  and  most  moist,  and  a  larger 
condensation  of  moisture  where  the  soil  is  dryer  and  cool- 
er. Even  where  there  is  little  difference  in  temperature  be- 
tween adjacent  layers  of  soil  there  must  be,  if  they  are  not 
equally  saturated,  a  tendency  for  diffusion  to  take  place 
more  rapidly  from  the  wettest  layer  of  soil  toward  that 
which  is  least  moist.  It  is  possible  that  during  dry  times 
and  in  dry  climates  during  the  dry  season  some  moisture, 
too  far  below  the  root  zone  to  be  made  available  through 
capillarity,  may  be  carried  upward  by  these  thermal  or 
evaporation  movements  so  as  to  become  helpful  to  crops  in 
a  measure.  We  are  yet  lacking  in  experimental  data  to 
form  any  just  conception  as  to  the  magnitude  of  such  a 
movement. 

209.  Temperature  Influence  of  Hygroscopic  Moisture. — It 
is  Hilgard's  view  that,  in  dry  climates  and  during  droughty 
periods  in  humid  climates,  the  moisture  still  retained  by 
soils  when  capillarity  has  become  very  feeble  may  exert 
an  important  influence  in  preventing  the  soil  from  becom- 
ing overheated  during  dry  soil  conditions,  by  the  cooling 
effect  of  internal  evaporation.  It  must  be  observed,  how- 
ever, that  in  order  that  this  influence  may  become  effective 
the  moisture  evaporated  must  have  left  the  soil  and  not 


ISO  Physics  of  the  Soil 

have  been  replaced  by  an  equal  amount  through,  condensa- 
tion from  some  other  place. 

It  appears  to  the  writer  possible  that  the  ability  of  such 
soils  to  withstand  drought  may  perhaps  be  partly  due  to 
a  more  rapid  evaporation  from  the  soil  grains  and  con- 
densation of  moisture  on  the  root  hairs,  the  thermal  move- 
ment, in  this  way,  tending  to  supplement  the  enfeebled 
capillarity. 


CHAPTER  VIII. 

CONSERVATION  OF  SOIL  MOISTURE. 

There  are  very  few  fields  upon  which  crops  of  any  kind, 
in  any  climate,  can  be  brought  to  maturity  with  the  max- 
imum yields  the  soils  are  capable  of  producing  without 
adopting  means  of  saving  the  soil  moisture.  There  are 
fields,  it  is  true,  where,  at  times,  the  moisture  in  the  soil 
is  too  great,  and  drainage  becomes  necessary;  but  even  un- 
der these  conditions  it  will  usually  be  found  advisable  to 
adopt  measures  for  conserving  the  water  not  so  removed. 

210.  Modes  of  Controlling  Soil  Moisture. — In  aiming  to 
control  soil  moisture  three  distinct  lines  of  operation  are 
followed,  based  upon  as  many  different  aims.     These  are: 

(1)  To  conserve  the  moisture  already  in  the  soil   (a) 
by  different  modes,  times  and  frequencies  of  tillage,  (b) 
by  the  application  of  mulches,    and    (c)    by   establishing 
wind  breaks. 

(2)  To  reduce  the  quantity  of  water  in  a  soil  (a)  by 
frequent  stirring,   (b)  by  ridging  or  firming  the  surface, 
(c)  by  decreasing  the  water  capacity,  and  (d)  by  surface 
or  under  drainage. 

(3)  To  increase  the  amount  of  water  in  a  soil   (a)  by 
increasing  its  water  capacity,    (b)   by   strengthening  the 
capillary  movement  upward  and  (c)  by  irrigation. 

211.  Late  Fall  Plowing  to  Conserve  Moisture — There  is 

no  method  of  developing  so  effective  a  soil  mulch  as  that 
furnished  by  a  tool  which,  like  the  plow,  completely  cuts 
off  a  layer  of  surface  soil  and  returns  it  loosely,  bottom 
up,  to  place  again. 


182  Physics  of  the  Soil. 

When  ground  is  plowed  late  in  the  fall,  just  before 
freezing,  it  then  acts  during  the  winter  and  early  spring 
as  a  mulch,  diminishing  the  loss  of  water  by  surface  evapo- 
ration, and  at  the  same  time  the  roughened  surface  tends 
to  hold  the  snows  and  to  permit  winter  and  early  spring 
rains  to  penetrate  more  deeply  into  the  soil,  leaving  tho 
ground  more  moist  at  seeding  time  than  would  be  the  case 
if  it  were  left  unplowed.  Determinations  of  the  moisture 
in  the  spring,  as  late  as  May  14,  have  proved  that  late  fall 
plowed  ground  may  contain  fully  6  pounds  per  square  foot 
more  water  in  the  upper  four  feet  than  similar  adja- 
cent ground  not  plowed.  This  difference  represents  a 
rainfall  of  1.15  inches  and  is  a  very  important  saving  in 
climates  of  deficient  water  supply  for  crops. 

212.  Late  Tillage  for  Orchards  and  Small  Fruits. — Late 
fall  plowing  and  deep   cultivation    in    orchards    of    fruit 
trees  and  in  vineyards  of  small  fruits,  after  the  wood  is 
fully  matured  and  growth  arrested  by  the  cold  weather, 
will  do  very  much  toward  giving  the  soil  better  moisture 
relations  the  next  spring,  tending  to  secure  such  results 
as  are  cited  in  (211).     In  cases  where  injury  from  deep 
freezing  is  liable  to  occur  the  late  plowing  will  lessen  this 
danger  because  the  loose  soil  blanket  will  help  to  retain 
the  heat  in  the  ground  as  well  as  the  soil  moisture. 

In  the  late  plowing  and  deep  tillage,  advised  in  this  and 
the  last  section,  there  is  little  danger  of  increasing  the  loss 
of  plant  food  by  leaching  because  the  season  is  too  late 
and  the  temperature  of  the  soil  too  low  to  stimulate  the 
formation  of  nitrates. 

213.  Early  Fall  Plowing  to  Save  Soil  Moisture. — In  those 
cases  where  winter  grain  is  to  be  sowed,  the  early  plowing 
of  the  ground,  or  plowing  as  soon  as  the  field  has  been 
freed  from  the  preceding  crop,  is  in  the  direction  of  econ- 
omy of  soil  moisture.     So  too  in  sub-humid  climates,  even 
where  winter  grain  is  not  to  be  sowed,  it  will  often  be 
desirable  to  plow  as  early  as  possible  in  order  to  retain 


Conserving  Soil  Moisture.  183 

soil  moisture  and  to  facilitate  the  entrance  of  the  fall  rains 
more  deeply  into  the  ground.  The  early  plowing  or  disk- 
ing in  these  cases  may  also  be  helpful  in  hastening  nitrifi- 
cation in  the  soil. 

It  is  the  strong  tendency  of  early  fall  plowing,  in  cli- 
mates where  there  is  plenty  of  soil  moisture  to  develop 
nitrates  and  where  there  is  much  rain  in  the  late  fall  and 
early  spring,  Which  has  led  to  the  sowing  of  "cover  crops" 
having  for  their  primary  object  the  locking  up  of  the  solu- 
ble plant  foods  to  prevent  them  from  being  lost  by  soil 
leaching ;  and  the  tendency  of  early  fall  plowing  to  dimin- 
ish surface  evaporation  and  thus,  in  wet  climates,  to  in- 
crease percolation  and  the  loss  of  plant  food  may  some- 
times make  this  practice  undesirable  in  such  cases. 

214.  Early  Spring  Plowing  to  Save  Soil  Moisture — In  all 

climates  where  there  is  a  tendency  of  the  soil  to  become 
too  dry  the  earliest  stirring  in  the  spring,  which  is  prac- 
ticable without  injuring  the  soil  texture,  is  in  the  direc- 
tion of  economy  in  most  cases  because,  at  this  season  of  the 
year,  the  effectiveness  of  tillage  in  conserving  soil  moisture 
is  greater  than  at  almost  any  other  time.  This  statement 
follows  from  (198),  where  it  is  shown  that  a  wet  soil  car- 
ries water  to  the  surface  much  more  rapidly  and  from  a 
greater  depth  than  a  dry  soil  can.  In  the  spring  the  soil 
at  the  surface  is  usually  not  only  wet  but  also  well  com- 
pacted, two  of  the  most  important  conditions  for  the  rapid 
movement  of  water  to  the  surface,  and  it  is  because  of 
these  that  early  and  deep  spring  tillage  is  so  important 
as  a  means  of  saving  soil  moisture. 

In  one  instance,  where  two  immediately  adjacent  pieces 
of  ground,  in  every  way  alike,  were  plowed  in  the  spring, 
7  days  apart,  it  was  found  that  the  earliest  plowed  ground 
contained,  at  the  time  the  second  piece  was  plowed,  a  lit- 
tle more  moisture  in  the  upper  four  feet  than  it  had  7  days 
before,  while  the  ground  which  had  not  been  plowed  had 
lost,  in  the  same  interval  of  time,  an  amount  of  moisture 
from  the  surface  four  feet  equal  to  1.75  inches,  a  full 


184 


Physics  of  the  Soil. 


Conserving  Soil  Moisture.  185 

eighth  of  the  rainfall  of  the  growing  season  of  that  lo- 
cality. 

Norwasthe  saving  of  moisture  the  only  advantage  gained 
by  the  early  plowing,  for  the  soil  plowed  last  had  dried  so 
extensively  as  to  become  very  hard  and  lumpy,  thus  great- 
ly increasing  the  labor  necessary  to  fit  it  for  planting. 

In  another  experiment  to  study  the  effectiveness  of 
early  as  compared  with  late  spring  plowing  in  conserving 
soil  moisture  Fig.  57  shows  how  evident  the  effects  were 
to  the  eye. 

215.  Disking  or  Harrowing  Where  There  is  Not  Time  to 
Plow. — It  often  happens  in  the  spring  that  hot  dry  winds 
come  on  when  there  is  not  opportunity  to  get  the  ground 
plowed  in  time  to  save  the  needed  moisture  and  prevent 
the  development  of  clods.       In  such  cases  the  use  of  tho 
disk  harrow,  or  even 'the  ordinary  spike  tooth  harrow,  will 
do  very  much  to  save  the  moisture  and  preserve  the  tiltli 
of  the  soil,  if  only  the  fields  are  gone  over  with  these.      The 
disk  harrow  is  one  of  the  best  of  tools  for  early  use  in 
the  spring  to  work  the  soil  and  develop  mulches. 

216.  Corn   and   Potato    Ground,    Orchards   and    Gardens 
Plowed  Early  in  the  Spring. — Ground  to  be  planted  to  corn 
or  potatoes,  as  well  as  the  orchard  and  garden,  should  gen- 
erally be  plowed  quite  early  in  the  spring  and  a  consid- 
erable time  before  it  is  intended  to  plant  them.     By  doing 
this,  not  only  will  moisture  be  saved  but  the  development 
of  nitrates  in  the  soil  will  be  hastened  and  thus  larger 
crops  secured  on  this  account.     It  is  only  in  the  event  of 
long,  frequent  and  heavy  rains,  following  such  early  tillage, 
that  loss  can  result  from  such  a  practice. 

217.  Effectiveness  of  Soil  Mulches. — The  effectiveness  of 
soil  mulches  as  means  for  diminishing  evaporation  varies 
(1)  with  the  size  of  the  soil  grains,  (2)  with  the  coarse- 
ness of  the  crumb  structure,  (3)  with  the  thickness  of  the 
mulch  and  (4)  with  the  frequency  with  which  the  soil  is 


186 


Physics  of  the  Soil. 


stirred.  Soils  which  maintain  a  strong  capillary  rise  of 
water  through  them  will,  when  converted  into  mulches, 
still  permit  the  water  to  waste  through  their  mulches  faster 
than  it  will  be  lost  through  the  mulches  of  soils  which 
permit  only  slow  capillary  movements.  That  is,  the  sandy 
soils  form  more  effective  mulches  than  do  the  clayey  ones 
and  this  greater  effectiveness  of  the  sandy  soils,  as  mulches, 
goes  a  long  way  toward  making  the  smaller  amount  of 
water  they  are  able  to  retain  effective  in  crop  production. 
In  Fig.  58  is  shown  an  apparatus  for  measuring  the 
relative  effectiveness  of  mulches  and  in  the  table  which 
follows  are  given  ths  results  of  a  series  of  trials  with 
three  types  of  soil.  The  cylinders  in  this  series,  however, 
stood  out  in  the  open  air  of  the  field  rather  than  in  the 
case  shown  in  the  cut. 

Table  showing  the  effectiveness  of  soil  mulches  of  different 
kinds  and  different  thicknesses. 


No  mulch, 
water   lost 
per  1UO 
days. 

Mulch 
1  in.  deep, 
water   lost 
per  100 
days. 

Mulch 
2  in.  deep, 
water   lost 
per  100 
days. 

Mulch 
3  in.  deep, 
water   lost 
per  100 
days. 

Mulch 
4  in.  deep, 
water    lost 
por  100 
days. 

Black  marsh  soil: 
Tons  per  acre  

588.0 

355.0 

270.0 

256.4 

252  5 

Inches  of  water    — 
Per   cent,  saved   by 

5.193 

3.12 
39.54 

2.381 
51.08 

2.265 
56  39 

2.230 
57  06 

Sandy  loam  : 
Tons  pur  acre  

741.5 

373.7 

339.3 

287.5 

315  4 

Inches  of  water  
Per   cent,  saved   by 
mulches  

6.548 

3.300 

49.69 

2.996 
54  24 

2.539 
61.22 

2.785 
57.47 

Virgin  clay  loam  : 
Tons  per  acre  

2,414. 

1.260. 

979.7 

889.2 

883  9 

Inches  of  water  
Per  cent,    saved   by 
mulches  

21.31 

11.13 

47.76 

8.652 
59.38 

7.852 
63.13 

7.  SOS 
63.34 

From  this  table  it  will  be  seen  that  the  soil  mulches  have 
exerted  a*very  great  influence  in  saving  soil  moisture. 


Conserving  Soil  Moisture. 


187 


It  should  be  understood,  however,  that  if  the  water 
reservoirs  had  been  much  farther  below  the  surface  of  the 
soil,  and  below  the  mulch,  the  mulches  would  have  been 
more  effective  as  well  as  less  water  would  have  been  lost 
from  the  unmulched  cylinders. 

218.  Frequency  of  Cultivation  May  Make  Mulches  More 
Effective. — When  a  fresh  mulch  is  formed  upon  the  surface 
of  a  well  moistened  soil  the  first  effect  of  the  stirring  is 


0 


k 


':••-  ] 


1 


[ 


:;:v| 


a 


FIG.  58.— Apparatus  for  measuring  the  relative  effectiveness  of  mulches. 

to  increase  the  rate  of  evaporation  from  the  field,  on  ac- 
count of  the  much  larger  surface  of  wet  soil  which  is  ex- 
posed to  the  air.  This  greater  loss  of  water,  however,  is 
largely  from  the  stirred  soil.  If  dry  winds  and  sunny 
weather  follow  the  formation  of  the  soil  mulch  it  soon 
becomes  so  dry  that  but  a  relatively  small  amount  of  wa- 
ter can  pass  up  through  it  On  the  other  hand  if  a  series 
of  cloudy  days  follow,  when  the  rate  of  evaporation 
must  be  small  even  from  firm  wet  soil,  and  if  at  the  same 
time  the  soil  below  the  mulch  is  quite  moist,  so  much  water 
may  pass  up  into  the  mulch  as  to  nearly  saturate  the 
lower  portion  of  it  and  to  cause  the  kernels  to  be  drawn 


188 


Physics  of  the  Soil. 


together  and  again  compacted  and  reunited  with  the  un- 
stirred soil  below.  If  this  change  does  take  place  the 
mulch  is  rendered  less  effective  and  a  second  stirring  is 
needed. 


FIG.  59.— Showing  large  cylinders  for  studying  soil  problems. 

The  relative  effectiveness  of  mulches  stirred  twice  per 
week,  once  per  week,  and  once  in  two  weeks,  for  a  virgin 
clay  loam,  in  cylinders  52  inches  deep  and  18  inches  in 
diameter,  standing  in  our  plant  house,  as  shown  in  Fig. 
59,  is  given  in  the  table  which  follows. 


Conserving  Soil  Moisture. 


189 


Table  showing  the  relative  effectiveness  of  soil  mulches  of  dif- 
ferent depths  and  different  frequencies  of  cultivation. 


Not  culti- 
vated. 
Per  acre. 

Once  in 
2  woi'ks. 
Per  acre. 

Oncrc  per 
week 
Per  acre. 

Twice  per 
week. 
Per  aero. 

Cultivated  one  inch  deep: 
The  loss  in  tons  per  100  days  was 
The  loss  in  inches  per  100  days 
was  

724.1 

6  304 

551.2 
4  867 

545.0 
4  812 

527.8 
4  662 

The  percentage  of  water  saved 
was  

23  88 

24  73 

27  10 

Cultivated  two  inches  deep  : 
The  loss  in  tons  per  10U  days  was 
The  loss  in  inches  per  10U  days 
was  

724.1 
6.394 

609.2 
5.380 

552.1 
4  875 

515.4 
4.552 

The  percentage  of  water  saved 
was  

15.88 

23.76 

28.81 

Cultivated  three  inches  deep: 
The  loss  in  tons  per  100  days  was 
The  loss  in  inches  per  100  days 
was  

724.1 
6.394 

612.0 
5.402 

531  5 

4.B94 

495.0 
4.371 

The  percentage  of  water  saved 
was  

15.49 

26  60 

31.64 

It  will  be  seen  that  with  each  of  the  three  depths  of  cul- 
tivation the  percentage  of  moisture  saved,  over  that  which 
was  lost  from  the  ground  not  cultivated,  increased  with  the 
frequency  of  cultivation. 

219.  Too  Frequent  Cultivation  "Undesirable. — When  a  soil 
mulch  is  well  loosened  and  thoroughly  separated  from  the 
firm  ground  beneath,  and  especially  after  the  mulch  has 
become  quite  dry,  little  can  be  gained  by  stirring  the  soil. 
Indeed  it  must  ever  be  kept  in  mind  that  it  costs  to  cul- 
tivate a  field  and  when  this  is  done  without  need  the  work 
is  a  dead  loss.  Further  than  this,  late  in  the  season,  when 
the  surface  of  the  ground  has  become  relatively  dry,  posi- 
tive harm  may  bo  done  by  unnecessary  cultivation  because 
at  this  season  many  plants  have  put  up,  very  close  to 
the  surface,  great  numbers  of  fine  roots  in  order  to 
avail  themselves  of  the  moisture  from  light  showers  and 
from  the  dew  which  may  be  condensed  in  the  surface  layer 


190  Physics  of  the  Soil. 

of  soil  on  the  coolest  nights.  To  destroy  these  roots  will, 
in  most  cases,  cause  a  greater  loss  by  root  pruning  than 
can  be  gained  by  saving  moisture.  It  is  possible  also,  by 
too  frequent  tillage,  to  make  the  texture  of  the  mulch  so 
fine  that  its  effectiveness  is  decreased. 

220.  Cultivations  Should  Be  Most  Frequent  in  the  Spring. 
In  the  early  part  of  the  season  when  the  aeration  of  the 
soil,  the  warming  of  it  and  the  killing  of  weeds  are  other 
important  objects  to  be  attained  it  is  more  important  to 
cultivate  frequently.     This  is  the  season  of  the  year  when 
the  effectiveness  of  mulches  decreases  most  rapidly,  it  is 
the  season  when  there  is  least  danger  of  destroying  the 
roots  of  the  crop,  and  it  is  the  time  when  cultivation  is 
needed  to  help  develop  plant  food. 

221.  Cultivation  After  Heavy  Rains — Whenever  a  rain 
has  occurred  which  has  thoroughly  united  the  soil  crumbs 
to  one  another,  and  with  the  soil  below,  it  is  time  to  cul- 
tivate again  if  this  can  possibly  be  done  without  too  heavy 
root  pruning,  and  the  cultivation  should  be  done  just  a3 
quickly  as  the  soil  will  permit.     In  the  early  part  of  the 
season  there  is  little  danger  of  root  pruning  if  the  culti- 
vator teeth  do  not  go  too  close  to  the  plants  and  not  more 
than  3  inches  deep. 

A  rain  which  does  not  wet  down  more  than  3  inches 
cannot  be  saved  by  cultivation;  all  that  can  be  done  in 
this  case  is  to  permit  the  surface  roots  to  get  as  much 
of  it  as  possible  and  to  stir,  if  it  appears  expedient,  when 
the  wetting  is  likely  to  strengthen  the  upward  movement 
too  much.  It  must  be  remembered  in  this  connection, 
however,  that  if,  late  in  the  season,  the  roots  of  the  crop 
have  spread  horizontally  through  the  whole  soil,  anything 
which  strengthens  the  rise  of  the  deeper  water,  causing 
it  to  come  nearer  the  surface,  at  the  same  time  brings  it 
to  the  roots  where  it  is  needed,  and  hence  it  will  seldom 
happen  that  a  crop  like  corn  or  potatoes  can  be  helped  by 


Conserving  Soil  Moisture.  191 

cultivation  after  the  corn  is  in  tassel  or  the  vines  begin  to 
well  cover  the  ground. 

222.  Depth  of  Cultivation  to  Save  Moisture. — In  regard 
to  this  point  it  must  be  kept  in  mind  that  the  soils  out  of 
which  mulches  are  made  are  the  richest  on  the  farm  and  that 
when  they  are  converted  into  perfect  mulches  they  are  prac- 
tically useless  so  far  as  direct  pknt  feeding  is  concerned. 
The  general  rule  must  then  be  to  make  the  mulch  just 
as  thin  as  it  can  be  and  not  permit  too  heavy  a  waste  oi 
the  deeper  soil  water. 

On  the  lighter  and  coarser  grained  soils  the  mulches 
may  be  shallower  than  on  those  of  the  clayey  type. 

In  Wisconsin  we  have  found  that  with  the  ordinary 
narrow  pointed  tooth  cultivators  a  depth  of  about  three 
inches  saves  more  moisture  and  permits  larger  yields  of 
corn  in  about  15  cases  out  of  20  than  less  depth  of  culti- 
vation. Where  the  tool  is  of  such  a  character  that  it 
shaves  off  the  whole  surface  of  the  ground  and  leaves  the 
stirred  soil  spread  in  a  blanket  of  uniform  thickness  the 
stirring  iriay  be  shallower  than  if  the  surface  of  the  ground 
is  left  in  either  narrow  or  wide  ridges. 

223.  Depth  and  Frequency  of  Cultivation  Should  Vary 
With  the  Season  and  Crop. — From  what  has  been  said  in  the 
preceding  paragraphs  it  follows  that  the  soil  may  to  ad- 
vantage   be    cultivated  more  deeply  and  more  frequently 
during  the  early  part  of  the  season  when  the  soil  tem- 
peratures tend  to  be  low,  when  the  moisture  may  be  over- 
abundant, and  when  weed  seeds  are  germinating.     Later 
in  the  season,  however,  when  there  is  not  as  great  need 
to  encourage  the  development  of  nitrates  by  tillage,  when 
the  roots  have  come  closer  to  the  surface,  and  the  main- 
tenance of  a  soil  mulch  is  the  chief  or  only  object,  the 
cultivation    may    evidently  be  less  deep  and  not  so  fre- 
quent.    The  general  practice  then  should  be  to  gradually 
make  the  cultivation  both  less  deep  and  less  frequent.     It 
should  also  be  kept  in  mind  that  cultivation  may  gener- 


192  Physics  of  the  SoiL. 

ally  be  a  little  deeper  in  the  middle  of  the  space  between 
rows,  than  close  to  the  hills,  because  of  less  danger  of  root 
pruning. 

224.  Best  Time  to  Cultivate  Corn  and  Potatoes — The  best 
time  to  till  land  for  corn,  potatoes  and  similar  crops,  where 
intertillage  is  practiced,  is  before  the  ground  is  planted 
and  just  as  the  crop  is  coming  up.     When  the  ground  is 
plowed  two  or  three  weeks  before  the  crop  is  to  be  planted 
there  is  opportunity  to  develop  the  nitrates,  to  kill  one 
or  two  crops  of  weeds,  and  to  store  in  the  upper  five  feet 
of  soil  the  largest  reserve  of  soil  moisture  from  the  spring 
rains.       Besides  these  advantages  there  is  no  period  in 
the  growth  of  the  crop  when  the  ground  can  be  stirred  so 
rapidly  and  so  cheaply.       Before  planting  the   disk  or 
spring-tooth  harrow  may  be  used  and  afterward  the  dif- 
ferent   weights    of    spike-tooth  harrows,  which  enable  a 
larger  area  of  ground  to  be  covered  in  a  day  by  a  man 
and  team.     The  harrowing  of  corn  and  potatoes  should 
be  continued  until  the  plants  are  well  out  of  the  ground 
and  if  care  is  taken  to  do  the  work  during  the  hot  por- 
tion of  the  day,  when  from  slight  wilting  the  plants  do 
not  break  off  readily,  there  need  be  but  little  serious  in- 
jury to  them. 

The  different  types  of  mulch  producing  tools  are  dis- 
cussed in  Chapter  XL 

225.  Harrowing  and  Rolling  Small  Grain  After  It  Is  Up. — 
It  sometimes  happens  in  humid    climates,    when    drying 
weather  follows  a  wet  period,  that  a  crust  forms  on  the 
surface  of  fields  sowed  to  the  small  grains,  which  may 
be  injurious  to  the  plants  by  preventing  sufficient  aera- 
tion and  increasing  the  loss  of  moisture.     In  such  cases 
the  difficulties  may  be  partly  corrected  by  using  either  the 
roller  or  the  light  harrow  with  teeth  sloping  backward. 

If  the  grain  is  large,  and  especially  if  the  surface  of 
the  field  has  been  left  narrowly  ridged  and  somewhat 
lumpy,  the  use  of  the  roller  when  the  surface  soil  is  dry 


Conserving  Soil  Moisture.  193 

will  break  up  the  crust  by  crumbling  down  the  ridges  and 
lumps  and  at  the  same  time  develop  a  true  and  effective 
mulch.  The  light  harrow,  when  driven  across  the  ridges, 
may  be  effective  in  breaking  up  the  crust  and  in  develop- 
ing a  mulch. 

In  sub-humid  climates,  such  as  that  of  western  Kansas, 
fields  seeded  permanently  to  alfalfa  have  been,  in  the 
very  early  spring,  gone  over  with  the  disk  harrow  and 
then  crossed  with  the  spike-tooth  harrow,  thus  developing 
a  very  effective  mulch  which  materially  increases  the  yield. 

226.  Mulches  Not  Made  From  Soil — While  it  is  true  that 
most  conservation  of  moisture  must  be  through  earth 
mulches  it  should  be  understood  that  all  vegetation  growing 
upon  the  ground,  whether  it  completely  covers  the  surface 
or  not,  exerts  a  protective  influence  and  diminishes  the 
loss  of  moisture  directly  from  the  soil  itself.  This  pro- 
tection comes  partly  from  shading,  partly  from  diminish- 
ing the  wind  velocity  and  partly  from  the  saturation  of 
the  air  with  moisture  by  the  transpiration  from  the  grow- 
ing plants. 

Even  in  pastures  where  the  grass  is  short,  but  close,  the 
mulching  effect  is  strong  and  hence  it  is  not  in  the  direc- 
tion of  economy  to  allow  the  feeding  to  be  too  close,  not 
only  because  the  growth  of  the  grass  is  slower  from  too 
severe  destruction  of  the  foliage,  but  because  there  is  a 
greater  loss  of  soil  moisture  besides  that  passing  through 
the  grass. 

The  surface  dressing  of  meadows  with  farmyard  manure, 
thoroughly  harrowed  to  spread  it  evenly  over  the  ground, 
is  extremely  beneficial  through  its  mulching  effect  as  well 
as  in  the  plant  food  it  brings  to  the  soil.  When  such 
dressings  are  applied  in  the  winter  and  early  spring  and 
spread  over  the  surface  while  the  soil  is  yet  wet  beneath, 
the  saving  in  soil  moisture  is  greatest  and  in  the  case  of 
meadows  where  the  clover  has  disappeared,  for  any  rea- 
son, such  a  dressing  may  make  it  possible  to  get  a  new 
seeding,  by  sowing  the  clover  broadcast  before  the  frost 


194  Physics  of  the  Soil. 

is  out  in  the  spring,  so  that  the  thawing  and  freezing  will 
tend  to  cover  the  seed  and  the  thin  mulch  protect  the 
ground  from  too  rapid  drying  until  the  young  plants  are 
well  rooted. 

The  use  of  straw  and  other  coarse  litter  and  coarse  sand 
for  mulching  will  generally  only  be  practicable  in  gardens 
and  orchards  and  for  the  protection  of  shade  trees  and 
the  like. 

227.  Ridged  and  Flat  Cultivation. — It  used  to  be  a  com- 
mon practice  to  "lay  by"  the  corn  and  potato  crop  with 
a  strong  hilling  of  the  rows.  This  practice,  however,  ex- 
cept for  potatoes,  is  now  generally  abandoned  unless  in 
localities  where  surface  drainage  is  needed.  The  general 
abandonment  of  the  practice  rests  in  part  upon  the  be- 
lief that  the  evaporation  from  the  soil  is  appreciably  in- 
creased by  this  process  on  account  of  the  greater  amount 
of  surface  exposed  to  the  air. 

In  making  a  practical  test  during  the  season  of  1899 
the  results  recorded  in  the  following  table  were  secured. 

These  plots,  each  seven  rows  wide,  alternated  across  a 
field  of  nearly  uniform  soil  and  samples  were  taken  under 
and  between  every  row.  It  will  be  seen  that  the  soil  re- 
ceiving the  flat  cultivation  contained  at  the  end  of  the 
growing  season  a  little  less  water  than  the  ridged  plots, 
which  is  contrary  to  the  accepted  belief.  Since  the  ridges 
are  all  shaded  by  the  potato  vines  and  since  the  wind  cur- 
rents may  be  supposed,  to  be  less  strong  between  the  fur- 
rows, perhaps  this  is  as  should  be  expected.  It  is  true, 
however,  that  the  plots  cultivated  flat  produced  a  little 
larger  yield  per  acre  and  on  this  account  the  soil  should 
have  lost  more  moisture.  It  may  be  that  the  flat  cul- 
tivation did  really  make  a  larger  saving  of  water  and  that 
this  saving  was  the  cause  of  the  larger  yield. 


Conserving  Soil  Moisture. 


195 


Table  showing  the  water  content  of  soil,  Sept.  19,  under  and 
between  rows  of  potatoes  hilled  and  left  flat  when  laid  by. 


DEPTH  OF  SAMPLE. 

Nos.  of 
sub- 
plots. 

HILLED. 

FLAT. 

In  row. 

Between 
row. 

In  row. 

Between 
row. 

Firstfoot  \ 

1..  . 

Per  cent. 
12.83 
12.01 

Per  cent. 
14  11 
13.61 

Per  cent. 
11.85 

12.18 

Per  cent. 
14.23 
13.54 

2  
3    ... 

Mean  — 
1  .. 

12.42 

13.86 

12.02 

13.89 

16.71 
15.84 

IN.  56 

17.85 

15.  H8 
16.03 

17.69 
17.84 

2  

Third  foot    j 

3  

Mean  — 
1... 

16.28 

18.21 

15.71 

17.77 

18.00 
17.09 

18.61 
17.55 

16.41 
16.13 

18.03 
17.97 

2  

Fourth  foot  ] 
Mean  of  four  feet  

3    

Mean  — 
1  .. 

17.55 

18.03 

16.27 

18  00 

15.78 
14.41 

16.95 
13.98 

9.79 
13.08 

11.75 

14.01 

2  
3  

Mean  — 

15.06 
15.33 

15.46 
16.40 

11.44 
13.86 

12.88 
15.64 

228.  Subsoiling  to  Save  Soil  Moisture. — The  deep  -plowing 
or  stirring  of  the  soil,  to  which  this  name  has  been  applied, 
lias  the  effect  of  making  a  larger  per  cent,  of  the  rainfall 
available  in  producing  crops,  but  it  will  never  have  the 
wide  applicability  that  is  possible  for  surface  tillage.  In 
sub-humid  climates  where  the  subsoils  are  less  liable  to  be 
puddled  and  where  there  is  the  greatest  need  of  economy 
this  method  of  conserving  soil  moisture  will  find  its  widest 
usefulness. 

A  piece  of  ground  when  subsoiled,  as  represented  in 
Fig.  60  and  given,  with  an  adjacent  area,  a  like  amount 
of  water,  and  protected  from  surface  evaporation,  was 
found  to  have  retained  not  only  the  water  given  it  but  to 
have  gained  an  additional  supply  through  capillarity  from 
below-  while  the  ground  not  subsoiled  lost  a  large  per 
cent,  of  that  given  to  it  through  percolation  and  capillary 


190 


Physics  of  the  Soil. 


creeping.  From  the  subsoiled  area  8  inches  of  the  surface 
were  removed,  the  subsoil  spaded  to  a  depth  of  13  inches 
more,  and  the  soil  returned  to  its  place.  After  taking 


FIG.    60.—  Alethod    of    demonstrating    the    influence    of    subsoiling    on    soil 

moisture. 

samples  from  the  five  places  indicated  by  the  dots,  1.36 
inches  of  water  \vere  gradually  sprinkled  over  the  two 
areas  on  June  llth  and  they  were  allowed  to  remain  cov- 
ered until  the  15th,  when  samples  were  again  taken.  The 
changes  in  the  water  content  of  the  soil  in  the  two  areas 
are  shown  in  the  table  which  follows: 


Table  showing  the  ability  of  subsoiled  ground  to  hold  water 
against  gravity. 


Subsoiled. 

Not 
subsoiled. 

Difference. 

The  first  foot  gained  

Lbs. 
124.6 

Lbs. 
102.1 

Lbs. 
+92  5 

12  57 

10  34 

+62  23 

The  third  foot  sained  

38.22 

12.05 

+26  17 

33  26 

3  82 

+29  43 

The  fifth  foot  lost  

2.29 

19.5 

—17  21 

26S  65 

128  31 

254.41 

251  41 

Difference  

+14.24 

—126  1 

Conserving  Soil  Moisture. 


197 


The  subsoiled  ground  had  therefore  not  only  retained 
all  the  water  added  but  it  had  gained  by  capillarity  14.24 
Ibs.  more.  It  is  noteworthy  too  that  the  fifth  foot  in  both 
places  had  lost  water  upward  by  capillarity,  2.29  Ibs.  in 
the  former  and  19.5  Ibs.  in  the  latter  case. 

The  effect  of  subsoiling  on  the  capillary  rise  of  water 
from  below  was  demonstrated  by  using  the  same  piece  of 
apparatus  in  the  same  way  except  that  the  two  areas  were 
covered  to  prevent  evaporation,  without  adding  any  water, 
the  experiment  extending  from  June  26  until  July  2,  giv- 
ing the  results  shown  in  the  next  table. 

Table  showing  the  effect  of  subsoiling  on  the  capillary  rise  of 
water  from  the  deeper  soil  when  no  evaporation  can  take 
place  from  the  surface. 


ON  SUBSOILED  GROUND. 

1st  foot. 

2nd  foot. 

3rd  foot. 

4th  foot. 

5th  foot. 

June  26  (Moisture  ( 

Per  ct. 
23.29 

22.66 

Per  ct. 

21.89 

22.50 

Per  ct. 
17.85 

17.49 

Per  ct. 
14.14 

14.45 

Per  ct. 
19.55 

20.27 

•  ?    at  start    ( 
July  2  I  Moisture   ( 

(   at  close.  < 
Change  

—  .63 

+  .61 

—  .36 

+  .31 

+  .72 

June  26—  start  

ON  GEOUND  NOT  SUBSOILED  . 

22.52 
^3  97 

2C.67 
22.09 

17.74 
18.92 

15.06 
14  62 

19.34 
18.33 

July  2  —  close  

+1.45 

+1.32 

+1.18 

-  .44 

It  will  be  seen  that  in  the  subsoiled  area  there  had  been 
but  little  change  in  the  water  condition  while  the  ground 
not  subsoiled  had  gained  a  very  material  amount  of  water 
in  the  surface  three  feet  at  the  expense  of  that  deeper  in 
the  ground,  the  gain  in  the  upper  three  feet  amounting, 
on  the  36  square  feet,  to  129.69  Ibs.,  53.52  Ibs.  having 
come  from  the  fourth  and  fifth  feet  and  the  balance  prob- 
ably partly  from  the  sides  and  partly  from  the  sixth  foot. 

When  the  ground  was  subsoiled  in  the  same  manner  as 
13 


198 


'Physics  of  the  Soil. 


before  and  allowed  to  stand  exposed  under  natural  condi- 
tions, and  the  surface  kept  free  from  weeds  by  shaving 
them  off  close  to  the  surface  with  a  sharp  hoe,  it  was  found, 
after  an  interval  of  75  days  from  June  until  September, 
that  the  water  content  of  the  soil  stood  as  in  the  next  table. 
In  this  case  the  surface  foot  of  subsoiled  ground  is  dryer 
than  that  not  so  treated,  but  the  second,  third  and  fourth 
have  gained  in  moisture,  over  and  above  that  lost  from  the 
other  two  feet,  enough  to  represent  a  rainfall  of  1.G4 
inches. 


Subsoiled 
ground 

Not   subsoiled 
ground. 

Difference. 

Firstfoot  

Per  cent. 
17.07 

Per  cent. 
18  91 

Per  cent. 
—1.84 

S  -cond  foot  

23.29 

19.42 

+3.87 

Third  foot      

22.76 

17.78 

+4.98 

Fourth  foot  

16  35 

14.19 

+2.16 

Fifth  foot  

18.14 

19.20 

—1.06 

229.  Moisture  Effects  of  Subsoiling. — The  results  which 
have  been  given  in  the  last  section  illustrate  several  verj 
distinct  effects  produced  by  subsoiling: 

(1)  Subsoiling  increases  the  percentage  capacity  of  the 
soils  stirred  for  moisture. 

("2)  Subsoiling  decreases  the  capillary  conducting  power 
of  the  soil  stirred. 

(3)  Subsoiling  increases  percolation  through  the  soil 
stirred  or  its  gravitational  conducting  capacity. 

230.  How  Subsoiling  Increases  the  Water  Capacity  of  the 
Soil  Stirred. — When  a  soil  is  broken  into  lumps  lying  loosely 
together,  and  these  become  filled    with    water,    each    one 
behaves  in  a  measure  much  as  if  it  were  standing  by  it- 
self and  much  as  a  lump  of  sugar  would,  plunged  into 
water  and  then  withdrawn,  coming  forth  with  its  pores 
practically  filled  with  water.       In  short  columns  of  soil, 
like  the  lumps,  the  surface  films  of  water  which  span  their 
capillary  pores  are  strong  enough  to  maintain  their  whole 


Conserving  Soil  Moisture.  199 

interior  nearly  full  of  water,  drainage  being  largely  con- 
fined to  those  passageways  a"nd  cavities  which  have  largei 
than  capillary  dimensions. 

If  a  dozen  strands  of  candle-wicking,  two  feet  long,  are 
twisted  loosely  together,  saturated  in  a  basin  of  water,  and 
then  held  horizontally  from  the  two  ends  to  drain,  more 
water  will  be  retained  than  if  it  is  allowed  to  sag  into  a 
loop  and  drainage  from  it  will  be  still  more  complete  when 
hanging  from  one  end.  So  it  is  with  long  continuous  col- 
umns of  soil;  from  them  the  drainage  is  more  complete 
than  from  shorter  ones. 

231.  How  Subsoiling  Decreases  the  Capillary  Conducting 
Power. — When  large  open  spaces  have  been  formed  in  a 
soil,  by  any  means,  as  is  the  case  in  subsoiling,  every  such 
cavity  cuts  off  the  capillary  connection  with  the  unstirred 
soil  below  and  above  and  in  this  way  reduces  the  number 
of  capillary  passageways  by  which  water  may  rise  to  the 
surface.     This  being  true,  when  rains  fall  upon  subsoiled 
ground,  water  travels  downward  quite  slowly  until  after  it 
has  become  capillarily  saturated  and,  if  the  rain  is  not 
enough  to  over-saturate  the  layer,  the  whole  will  be  retained. 

On  the  other  hand,  when  the  subsoiled  layer  has  once 
become  dry,  the  poor  connection  with  the  firmer  ground 
below  and  its  open  texture  makes  it  impossible  for  the 
moisture  to  rise  through  it  to  the  surface  as  rapidly  as  it 
could  through  a  more  compact  layer. 

It  is  clear,  from  these  relations,  that  when  the  root 
system  of  a  crop  once  develops  through  the  subsoiled  layer 
it  may  then  act  as  a  mulch  of  great  thickness  and  increase 
the  yield ;  but  should  a  crop  fail  to  get  its  roots  below  the 
subsoiled  layer  before  the  moisture  becomes  too  scanty 
then  a  diminished  yield  might  be  the  result  even  with  an 
abundance  of  water  below. 

232.  How   Subsoiling   Favors   Percolation When    rain 

enough  has  fallen  upon  an  earth  mulch  or  upon  subsoiled 
ground  to  completely  saturate  the  soil  the  balance  of  the 


200  Physics  of  the  Soil. 

water  is  then  free  to  move  rapidly  downward  through  the 
large  non-capillary  pores,  urged  by  the  strong  force  of 
gravity.  Not  only  this,  but,  since  the  pores  are  many  of 
them  too  large  to  be  filled  by  the  percolating  streams,  there 
is  left  an  easy  egress  for  the  soil-air,  which  must  escape 
upward  before  the  water  can  enter,  and  this  does  not  re- 
tard percolation  as  it  does  in  a  compact  soil. 

233.  A  larger  Percentage  of  the  Moisture  of  Subsoiled 
Ground  Available  to  Crops. — When  a  soil  has  been  made 
more  open  by  subsoiling,  and  its  capacity  for  holding  water 
thereby  increased,  this  extra  amount  of  water  retained  be- 
comes wholly  available  to  crops.     It  was  shown  in  (161) 
and  (162)  that  there  is  a  certain  per  cent,  of  water  in  a 
soil  which  the  roots  of  plants  are  unable  to  remove  with 
sufficient  rapidity  to  meet  their  needs  and  as  this  amount 
depends  upon  the  size  of  the  soil  grains,  which  subsoiling 
does  not  alter,  the  increased  percentage  held  becomes  a 
clear  gain  to  the  crop. 

234.  Dangers  From  Subsoiling — One  of  the  most  serious 
difficulties  associated  with  subsoiling,  aside  from  the  ex- 
pense, is  the  danger  of  puddling,  and  this  is  particularly 
great  in  humid  climates  where  the  subsoil,  especially  in 
the  spring,  is  liable  to  be  too  wet.     The  danger  is  intensi- 
fied on  account  of  the  fact  that  the  surface  soil  may  be 
in  good  condition  for  plowing  when  that  below  is  much  too 
wet.     If  this  work  is  attempted  when  the  ground  is  not  in 
condition  very  great  harm  may  be  done  and  so  it  is  gen- 
erally much  safer  to  subsoil  late  in  the  fall  in  humid  cli- 
mates, when  the  deeper  ground  is  generally  dryest. 

235.  Early  Seeding — When  the  crop  is  started  to  grow- 
ing upon  the  ground  as  early  as  the  temperature  of  the 
soil  and  of  the  air  will  permit  the  farmer  is  conserving  soil 
moisture,    by  taking  advantage    of  that  which   otherwise 
would  be  lost  by  surface  evaporation,  and  enabling  his  crop 
to  use  this  in  growth.     Such  timely  planting  may  not  only 


Conserving  Soil  Moisture. 


201 


save  moisture  from  going  to  waste,  both  by  evaporation 
and  by  percolation,  but  it  may  save  plant  food  from  loss 
in  the  drainage  waters. 

Yet,  while  due  diligence  should  be  exercised  in  timely 
planting  and  sowing,  there  is  danger  of  too  great  haste  and 
it  will  generally  be  better  to  make  the  mistake  of  getting 
the  crop  in  a  little  late  rather  than  too  early.  The  soil 
should  by  all  means  be  warm  enough  and  dry  enough  to 
make  germination  prompt  and  vigorous,  for  otherwise  weak 
and  sickly  plants  will  result,  if  the  seed  does  not  rot  in 
the  ground. 

236.  Danger  From  Green  Manuring. — In  the  practice  of 
growing  cover-crops,  and  in  green  manuring,  attention 
must  always  be  given  to  the  effect  these  have  upon  the  soil 
moisture,  as  related  to  the  crop  which  is  to  follow.  When 
either  rye  or  clover  is  used  in  green  manuring,  and  the 
plants  are  allowed  to  make  a  heavy  growth  before  plowing 
under,  the  soil  will  be  found  very  much  dryer  than  if  the 
field  had  been  plowed  and  tilled  early  but  left  naked,  or 
even  if  not  plowed  at  all.  The  next  table  demonstrates 
the  truth  of  this  statement,  showing,  as  it  does,  the  strong 
drying  effect  of  clover  as  early  as  May  13. 

Table  showing  the  drying  effect  upon  the  soil  of  a  green  ma- 
nure crop. 


1  to  6  inches. 

n  to  18  inches. 

18  to  21  inches. 

Per  cent. 
23  33 

Per  cent. 
19  13 

Per  cent. 
16  85 

Ground  in  clover.  .................. 

9  59 

14.75 

13  75 

13  74 

4.38 

3  10 

In  such  a  case  as  this,  with  the  soil  as  dry  when  plowed 
as  that  under  the  clover,  not  only  would  there  be  danger 
of  the  seed  not  germinating  properly  but  the  large  growtli 
of  herbage,  when  plowed  under,  would  so  much  cut  off 
the  capillary  connection  with  the  deeper  soil  moisture  that 


202  Physics  of  the  Soil. 

it  could  not  readily  become  available  until  after  the  roots 
had  penetrated  below  this  level. 

Nor  is  this  all ;  any  such  crop  would  have  locked  up  in 
insoluble  form,  for  the  time  being,  a  large  portion  of  the 
soluble  plant  food,  and  unless  abundant  and  timely  rains 
were  to  follow  the  plowing  speedily  to  develop  a  new  sup- 
ply, the  next  crop  would  suffer  for  lack  of  nitrates  and 
other  plant  foods. 

On  soils  naturally  too  wet  and  in  wet  seasons  the  dan- 
gers referred  to  will  of  course  not  be  so  great  and  the 
green  manure  crop  might  even  be  an  advantage  from  the 
soil  moisture  side  by  making  the  over-wet  soil  more  open, 
thus  favoring  stronger  root  action  and  more  rapid  nitri- 
fication. 

237.  Wind-breaks  and  Hedges.  —"In*  sub-humid  climates, 
especially  like  those  of  our  western  prairies,  where  there 
is  a  high  mean  wind  velocity,  and  in  the  level  districts 
of  humid  climates,  where  the  soils  are  light  and  sandy,  with 
a  small  water  capacity,  and  which  are  lacking  in  adhesive 
quality,  the  fields  may  suffer  greatly  at  times,  not  only 
from  excessive  less  of  moisture,  but  the  soil  itself  may  be 
greatly  damaged  by  drifting  caused  by  the  winds.  Under 
such  conditions,  it  is  a  matter  of  great  importance  that  the 
wind  velocities  close  to  the  surface  should  be  reduced  as 
much  as  possible." 

On  the  lighter  sandy  lands,  wherever  broad  fields  lie 
unsheltered  by  any  wind-break,  strong  dry  winds  frequent- 
ly sweep  entirely  away  crops  of  grain  after  they  are  four 
inches  high,  and  at  the  same  time  drift  away  even  as  much 
as  three  or  four  inches  of  the  surface  soil,  the  best  in  the 
field.  In  such  cases  wind-breaks  and  hedge-rows  exert  a 
very  strong  protective  influence  and  greatly  lessen  such  dis- 
astrous results. 

Not  only  do  trees  along  line  fences  and  roadsides,  un- 
der these  conditions,  prevent  such  direct  injuries  to  soil  and 

•  Irrigation  and  Drainage,  p.  163. 


Conserving  Soil  Moisture.  203 

crops  but  they  materially  lessen  the  evaporation  of  moisture 
from  the  soil  and  thus  help  to  secure  a  higher  yield  of 
crops.  *"The  writer  has  observed  that,  when  the  rate  of 
evaporation  at  20,  40,  and  60  feet  to  the  leeward  of  a 
grove  of  black  oak  15  to  20  feet  high  was  11.5  c.  c.,  11.6 
c.  c.,  and  11.9  c.  c.,  respectively,  from  a  wet  surface  of 
27  square  inches,  it  was  14.5,  14.2  and  14.7  c.  c.,  at  280, 
300  and  320  feet  distant,  or  24  per  cent,  greater  at  the 
three  outer  stations  than  at  the  nearer  ones.  So,  too,  a 
scanty  hedge-row  produced  observed  differences  in  the  rate 
of  evaporation  as  follows,  during  an  interval  of  one  hour ; 

At  20  feet  from  the  hedge-row  the  evaporation  was 10.3  c.  c. 

At  350  feet  from  the  hedge-row  the  evaporation  was 12.5  c.  c. 

At  300  feet  from  the  hedge-row  the  evaporation  was 13.4  c.  c. 

Here  the  drying  effect  of  the  wind  at  300  feet  was  30 
per  cent,  greater  than  at  20  feet,  and  7  per  cent,  greater 
than  at  150  feet  from  the  hedge. 

Then,  too,  when  the  air  came  across  a  clover  field  780 
feet  wide  the  observed  rates  of  evaporation  were : 

At   20  feet  from  clover 9.3  c.  c. 

At  150  feet  from  clover 12.1  c.  c. 

At  300  feet  from  clover 18     c.  c. 

Or  40  per  cent  greater  at  300  feet  away  than  at  20  feet, 
and  7.4  per  cent,  greater  than  at  150  feet" 

*  Irrigation  and  Drainage,  p- 109. 


CHAPTER 
BELATION  OF  AIR  TO  SOIL. 

NEEDS  OF  SOIL  VENTILATION. 

.  Air  in  the  soil  in  which  crops  are  to  be  grown  is  as  es- 
sential to  the  life  of  the  plants  as  the  air  in  a  stable  is 
to  the  life  of  the  animals  housed. 

Careful  observations  and  lines  of  experimentation  have 
proved,  in  many  ways,  that  when  oxygen  is  completely  ex- 
cluded from  seeds  that  are  otherwise  under  good  conditions 
for  germination  they  fail  to  start.  It  has  been  found,  too, 
that  even  after  a  seed  has  begun  to  grow,  if  the  oxygen 
supply  is  cut  off,  it  makes  no  farther  progress.  Growth 
does  take  place  in  seeds  in  a  very  dilute  atmosphere  of  oxy- 
gen, but  after  the  amount  has  been  reduced  below  »L2  of 
the  average  in  the  air  the  plants  advance  very  slowly  and 
are  sickly. 

A  soil  in  the  best  condition  for  crops  must  permit  of 
ready  entrance  of  fresh  air  and  an  abundant  escape  of 
the  air  once  used;  in  other  words,  like  the  stable,  it  must 
be  well  ventilated.  This  ventilation  is  needed : 

(1)  To  supply  free  oxygen  to  be  consumed  in  the  soil. 

(2)  To  supply  free  nitrogen  for  the  use  of  the  free- 
nitrogen-fixing  germs. 

(3)  To  remove  the  excess  of  carbon-dioxide  which  is 
set  free  in  the  soil. 

238.  Needs  For  Free  Oxygen  in  the  Soil. — Free  oxygen  in 
the  soil  is  required  not  only  by  the  seeds,  when  they  are 
germinating,  but  throughout  the  active  life  of  the  plant 
in  order  to  permit  the  roots  to  live,  for  they,  too,  must 
breathe. 

Then  in  the  conversion  of  the  nitrogen  of  humus,  manure, 


Needs  of  Soil  Ventilation.  205 

and  decaying  organic  matter  in  the  soil  into  nitric  acid, 
large  amounts  of  oxygen  are  needed,  for  each  of  the  three 
known  forms  of  microscopic  life  which  do  this  work  are 
unable  to  live  in  its  absence. 

239.  A  Water-logged  Sott — One  of  the  chief  reasons  for 
the  unproductiveness  of  a  water-logged  soil  is  the  deficiency 
of  free  atmospheric  oxygen  in  it.  When  the  soil  pores  are 
filled  with  water  and  this  water  is  stationary,  that  is,  not 
changing,  the  free  oxygen  which  it  may  contain  in  the  air 
dissolved  in  it  is  soon  used  up  and  then  the  rate  at  which 
oxygen  from  the  air  above  the  soil  is  able  to  make  its  way 
downward  through  the  soil-water  and  around  and  between 
the  soil  grains  is  much  too  slow  to  meet  the  ordinary  needs 
of  the  roots  of  any  crop.  Not  only  this,  but,  as  pointed 
out  in  (103),  even  the  microscopic  organisms  in  the  soil 
find  so  scanty  a  supply  that  they  are  obliged  to  decompose 
the  nitric  acid  for  the  oxygen  it  contains  in  order  to  supply 
their  needs.  The  chief  need  of  draining  wet  lands,  then, 
is  to  secure  to  the  soil  a  more  rapid  change  of  air. 

240.  Floating  Gardens. — The  instances  where  the  Chinese 
and  Mexicans  grow  crops  upon  floating  rafts  of  logs  an- 
chored in  a  stream  or  lake  and  thinly  covered  with  soil 
may  seem  to  contradict  the  statements  in  the  last  paragraph 
regarding  a  water-logged  soil  because,  in  these  cases,  the 
soil  is  very  wet  in  its  lower  portion  and  the  roots  of  the 
plants  are  continually  immersed  in  a  saturated  soil  or  in 
the  water  itself  beneath.  A  little  reflection,  however,  will 
make  it  clear  that  the  two  cases  are  very  different.  Both 
in  the  lake  and  in  the  running  stream  the  water  is  chang- 
ing continually  so  that  a  new  supply,  charged  with  fresh 
\  oxygen,  is  being  continually  brought  to  the  roots  or  very 
near  them. 

It  is  the  abundance  of  oxygen  which  rain  water  and 
that  used  for  irrigation  contains  which  prevents  it  from 
killing  crops  when  the  water  entering  the  soil  is  excessive. 
As  long  as  the  water  is  moving  through  the  soil,  and  a 


206  Physics  of  the  Soil. 

fresh  supply  from  above  entering,  an  abundance  of  air 
is  carried  with  it  for  the  needs  of  the  roots. 

241.  Excessive  Soil  Ventilation. — The  higher  temperature 
of  a  pile  of  open  horse  manure,  as  compared  with  that  of 
the  closer  heap  of  cow-dung,  illustrates  how  important  the 
free  and  rapid  access  of  air  to  the  interior  is  to  the  forma- 
tion of  the  ammonia,  for  the  difference  in  temperature  in 
the  two  cases  is  largely  due  to  a  difference  in  the  rate  of 
fermentation,  and  this  to  the  too  rapid  entrance  of  air. 
In  these  cases  the  air  is  entering  too  rapidly  and  a  loss 
of  nitrogen  is  the  result.     And  the  same  thing  may  occur 
in  a  too  open  soil.     Indeed,  the  small  amount  of  humus  in 
the  sandy  soils  is  in  a  large  measure  due  to  the  freer  ac- 
cess of  air  to  the  interior. 

It  is  for  this  reason  that  unusual  care  must  be  exercised 
to  keep  the  supply  of  humus  in  these  soils  up,  not  only 
because  of  its  need  for  plant  food,  but  because  it  enables 
the  sandy  soils  to  hold  more  water,  and  this  in  turn  makes 
them  less  readily  penetrated  by  the  air  and  the  humus  does 
not  waste  as  rapidly. 

242.  Return  of  Carbon-Dioxide  to  the  Air — It  is  of  course 
necessary  to  the  continuance  of  plant  life  that  the  vast 
systems  of  roots  which  are  developed  in  the  soil  should  be 
broken  down,  first  into  humus  and  then  into  carbon-dioxide, 
water  and  free  nitrogen,  and  all  of  the  processes  concerned 
in  these  changes  demand  free  oxygen  taken  from  the  air 
and  the  escape  of  the  carbon-dioxide  and  nitrogen  gas  set 
free,  and  here  again  is  ample  soil  ventilation  necessary. 

243.  The  Fixing  of  Free  Nitrogen — In  the  processes  of 
symbiosis  discussed  in  (101),  which  lead  to  the  removal  of 
the  free  nitrogen  of  the  air  in  the  soil  and  soil  moisture, 
and  the  conversion  of  it  into  organic  compounds  suitable 
for  the  food  of  higher  plants,  soil  ventilation  is  necessary 
in  order  to  supply  both  the  oxygen  and  nitrogen  of  the  air 
which  the  micro-organisms  are  obliged  to  use  in  carrying  on 
their  life  processes. 


Processes  of  Soil  Ventilation,.  207 


PROCESSES   OF   SOIL   VENTILATION. 

The  interchange  of  gases  between  the  soil  and  atmos- 
phere is  brought  about  in  several  ways  and  by  different 
agencies.  Among  these  are  (1)  the  slow  process  of  diffu- 
sion described  in  (5)  and  (14).  (2)  The  expansion  and 
contraction  of  soil-air  due  to  changes  in  temperature.  (3) 
The  expansion  and  compression  of  the  air  due  to  changes 
in  barometric  pressure.  (4)  The  suctional  effect  of  the 
wind,  especially  when  it  is  gusty.  (5)  The  air  absorbed 
by  rainwater  is  carried  into  the  soil  when  percolation  takes 
place.  (6)  When  water  drains  away  from  a  soil  or  is 
carried  upward  and  out  by  capillarity  or  root  action  it 
acts  by  suction  to  draw  into  the  soil  a  volume  of  air  equal 
to  that  of  the  water  which  flows  out. 

244.  Ventilation  of  Soil  by  Diffusion. — The  exchange  of 
air  between  that  in  the  soil  and  the  atmosphere  above  by 
diffusion  is  a  very  slow  process  but,  because  it  is  all  the 
time  taking  place,  the  total  exchange  during  the  growing 
season  is  considerable.     The  more  open  the  texture  of  the 
soil  is  and  the  higher  the  soil  temperature  the  more  rap- 
idly will  the  interchange  by  this  process  take  place. 

245.  Soil  Ventilation  Due  to  Changes  in  Soil  Tempera- 
ture.— When  the  temperature  of  air  is  changed  its  volume 
is  also  altered  and  in  the  ratio  of  rer    for    each    degree 
F.  or  -STS  for  each  degree  C.  ;  so  that  if  491  cubic  feet 

of  soil-air  were  to  have  its  temperature  changed  1°  F.  this 
would  result  in  one  cubic  foot  of  air  being  forced  out  of 
the  soil,  if  the  temperature  was  raised,  and  a  like  amount 
would  enter  if  the  temperature  were  to  fall  the  same 
amount. 

The  temperature  of  the  surface  three  inches  of  soil  often 
changes  as  much  as  16°  to  20°  F.  and  that  at  18  inches 
deep  as  much  as  1.5°  F.  A  soil  like  the  surface  foot  in 
(133),  containing  18  per  cent,  of  water,  would  enclose 


208  Physics  of  the  Soil 

about  5.3  acre-inches  of  air  in  the  surface  1.5  feet  and, 
with  a  diurnal  change  of  16.4°  F.  in  the  upper  '3  inches 
and  1.5°  F.  at  a  depth  of  18  inches,  the  amount  of  soil-air 
which  would  be  forced  out  and  again  taken  in  each  24 
hours  would  be  about  14  cubic  inches  for  each  square  foot 
of  surface.  So  that  the  soil  ventilation  due  to  diurnal 
changes  in  soil  temperature  will  range  from  0  up  to  pos- 
sibly 20  cu.  in.  per  square  foot. 

246.  Influences  of  Changes  in  Barometric  Pressure  on  Soil 
Ventilation. — Any  change  which  may  occur  in  the  pressure 
of  the  air  above  the  soil  is  followed  by  a  change  in  the 
volume  of  the  soil-air,  causing  an  escape  from  the  soil,  if 
the  pressure  above  falls,  and  the  entrance  of  an  extra  sup- 
ply whenever  the  pressure  is  increased. 

With  soil  like  that  in  (133),  having  18  per  cent,  of  water 
in  the  first  foot,  20  per  cent,  in  the  second  and  15  per 
cent,  in  the  third  and  fourth  feet,  there  would  be  7.88 
inches  in  depth  of  soil-air  contained  in  the  four  feet  and 
every  change  in  atmospheric  pressure  amounting  to  .1  incli 
would  cause  the  escape  or  entrance  of  3.78  cubic  inches 
for  each  square  foot  of  surface  and  18.9  cubic  inches  for 
each  change  in  pressure  of  .5  inches  of  barometer. 

It  is  common  in  the  United  States  for  waves  of  high 
and  low  pressure  to  pass  a  given  locality  about  twice  each 
week,  and  the  differences  in  pressure  between  high  and  low 
barometer  are  generally  not  far  from  .5  inch,  so  that  the 
results  stated  above  give  a  fair  measure  of  this  influence 
in  soil  ventilation. 

247.  Wind  Suction  and  Soil  Ventilation. — It  is  seldom 
true  that  the  wind  blowing  across  a  field  has  a  uniform 
velocity,  the  general  tendency  being  for  it  to  blow  in  gusts. 
This  unsteady  action  tends  at  times  to  increase  the  pres- 
sure on  the  soil-air  and  at  other  times   to    decrease    that 
pressure  and,  as  a  result,  there  is  a  nearly  constant  ten- 
dency for  air  to  leave  or  enter  the  soil  on  this  account, 
and  it  is  possible  that  this  factor  in  soil  ventilation  may 


Ways  of  Influencing  Soil  Ventilation.  209 

be  stronger  than  any  other,  on  account  of  the  great  fre- 
quency with  which  the  changes  recur. 

248.  Movements  of  Water  and  Soil  Ventilation. — The 
water  which  enters  the  soil  as  rain  must  displace  a  volume 
of  air  equal  to  the  rainfall  which  penetrates  the  soil  and 
then,  when  this  water  is  again  lost  by  the  soil,  whether 
by  percolation  or  by  capillary  or  root  action,  the  same  vol- 
ume of  air  must  again  be  returned.  In  a  climate  where 
the  rainfall,  which  penetrates  the  soil,  is  24  inches  dur- 
ing the  growing  season,  two  cubic  feet  of  air  per  square 
foot  of  surface  enters  the  soil  in  consequence. 


WAYS  OF  INFLUENCING  SOIL  VENTILATION. 

There  are  important  means  and  methods  of  controlling 
and  modifying  the  rate  and  extent  of  soil  ventilation, 
which  are  under  the  control  of  the  farmer. 

249.  Soil  Ventilation  Modified  by  Tillage. — Nearly  all  of 
the  operations  of  surface  tillage  modify  the  rate  of  entrance 
or  escape  of  air  from  the  soil.  Plowing  effects  a  sudden 
and  complete  change  of  air  in  the  soil  to  the  depth  stirred 
and  in  the  spring,  when  nitrates  are  deficient,  and  the 
pores  largely  closed  with  water,  this  breaking  up  of  the 
soil  may  be  very  beneficial. 

The  thorough  preparation  of  the  seedbed  before  plant- 
ing, so  strenuously  insisted  upon  by  the  best  practical  men, 
has  a  portion  of  its  rational  basis  in  the  need  of  soil  ven- 
tilation ;  and  deep  subsoiling,  when  done  at  such  a  time 
as  not  to  puddle  the  soil,  must  always  profoundly  affect 
the  relation  of  air  to  soil,  as  well  as  of  moisture.  Indeed, 
all  of  the  operations  of  soil  loosening  serve,  not  only  to 
admit  air  more  freely  to  the  soil  stirred,  but  the  undis- 
turbed portions  beneath  will  also  be  better  ventilated  be- 
cause of  the  surface  loosening. 


210  Physics  of  the  Soil. 

250.  Rolling  and  Harrowing  For  Soil  Ventilation. — It  fre- 
quently happens,  especially  with  small  grains  in  the  spring, 
when  the  season  has  been  unusually  wet  and  evaporation 
large,  that  a  crust  forms  upon  the  surface,  partly  by  shrink- 
age, partly  by  the  crumb-structure    breaking    down  and 
partly  by  the  deposit  of  soluble  salts  between  the  soil  grains, 
thus   closing   up   the   pores  and  greatly  impeding  the  en- 
trance of  air.     Under  such  conditions  the  harrowing  or 
rolling  of  small  grains  after  they  are  up  owes  its  advan- 
tages in  part  to  the  better  soil  breathing  it  secures,  by 
breaking  the  crust. 

But  it  will  sometimes  happen,  when  small  grains  are 
rolled  immediately  after  seeding,  if  the  ground  chances  to 
be  a  little  too  moist,  that  soil  ventilation  will  be  so  much 
hindered  by  the  packing  as  to  result  in  defective  germina- 
tion and  sickly  plants.  In  one  case  a  crop  of  barley  was 
so  much  affected  in  this  way  that  a  serious  reduction  of 
yield  was  the  result  and  the  plants,  even  when  mature, 
were  so  evidently  influenced,  that  the  rolled  strip,  between 
two  adjacent  areas  not  rolled,  but  in  other  respects  the 
same,  snowed  in  strong  contrast  on  account  of  the  smaller 
plants. 

251.  TJnderdraining  For  Soil  Ventilation. — When  heavy 
soils  are  underdrained  they  are  so  much  more  deeply  and 
better  aerated  that  this  is  one  of  the  chief  advantages  of 
that  method  of  land  improvement.     In  such  cases  the  roots 
of  plants  penetrate  the  subsoil  so  much  farther,  and  earth- 
worms and  ants  burrow  so  much  deeper,  that  with  the 
decay  of  the  roots  the  more  or  less  vertical  galleries  formed 
by  these  agencies  permit  much  freer  and  deeper  soil  ven- 
tilation. 

Then  when  the  under  clays  dry  out,  as  they  do  after 
draining,  great  numbers  of  shrinkage  checks  form  and  in- 
to these  both  the  roots  of  plants  and  the  free  soil-air  pene- 
trate and  are  brought  together. 

After  this  last  stage  of  soil  improvement  has  taken  place 
the  bringing  in  of  carbonic  acid  with  the  air  leads,  through 


Ways  of  Influencing  Soil  Ventilation.  211 

its  action  upon  the  lime,  to  the  flocculation  of  the  minuter 
soil  particles  and  thus  to  a  more  extensive  granulation  of 
the  whole  subsoil,  which  in  turn  extends  the  soil  ventilation 
still  more  widely. 

But  all  of  these  effects  upon  the  soil  are  only  the  means 
\vbich  permit  the  underdrains  to  render  their  greatest  serv- 
ice in  permitting  a  strong  and  extensive  movement  of  air 
into  and  from  the  soil ;  for  once  the  soil  is  opened  up  in  this 
way,  the  air,  through  the  action  of  the  wind,  changes  in 
barometric  pressure  and  changes  in  soil  temperature,  read- 
ily enters  the  soil,  not  only  through  the  surface  above  but 
throughout  the  whole  length  of  the  underdrains. 

When  it  is  seen  that  changes  in  soil  temperature  and  in 
atmospheric  pressure  make  such  marked  changes  in  the 
flow  of  water  from  springs  and  from  tile  drains  as  are 
shown  in  (337)  and  (338)  it  becomes  clear  that  the  move- 
ments of  soil-air  into  and  out  of  tile  drains  must  be  even 
more  marked  than  the  movements  of  ground  water. 

252.  Influence  of  Vegetation  on  Soil  Ventilation. — In  the 

case  of  such  crops  as  clover,  which  send  long  and  somewhat 
fleshy  roots  down  deeply  into  the  subsoil,  there  are  very 
many  and  important  passageways  opened  up  after  the  roots 
decay,  which  greatly  facilitate  the  deeper  and  more  rapid 
change  of  soil-air,  and,  as  has  been  pointed  out,  the  re- 
moval of  water  by  the- living  roots  must  also  draw  into  the 
soil  a  volume  of  air  equal  to  the  amount  of  water  used, 
except  in  so  far  as  this  is  made  good  by  the  rise  of  capil- 
lary water  from  below. 


CHAPTER   X. 
SOIL  TEMPERATUEE. 

253.  Importance  of  Soil  Temperature. — None  of  the  chem- 
ical, physical  or  biological  changes  essential  to  the  devel- 
opment of  plant  food  in  the  soil  and  to  the  action  of  roots, 
can.  take  place  in  the  absence  of  the  energy  stored  up  in 
the  soil  and  indicated  by  its  temperature.     When  the  tem- 
perature of  the  soil  falls  to   32°  F.  nearly  all  the  life 
processes  become  dormant  and  for  most  of  the  cultivated 
crops  and  higher  plants  these  cannot  begin  until  a  tem- 
perature above  40°  F.  has  been  reached.     All  living  bodies 
must  have  their  temperature  maintained  between  certain 
limits  in  order  to  have  growth  take  place. 

254.  Soil  Temperature  at  Which  Growth  Begins. — Accord- 
ing to  the  observations  of  Ebermayor  growth  will  not  be- 
gin, with  most  cultivated  cropsTtmtil  the  soil  has  attained 
a  temperature  of  45°  to  48°  F.  and  it  does  not  take  place 
most  vigorously  until  after  it  has  reached  68°  to  70°  F. 
Neither  do  the  niter  germs  begin  the  formation  of  nitric 
acid  from  humus  until  a  temperature  above  41°  F  has  been 
reached  and  its  greatest  activity  is  not  attained  until  the 
soil  temperature  has  risen  to  98°  F. 

255.  Best  Soil  Temperature  for  Germination — There  is, 
for  most  seeds,  a  certain  range  of  soil  temperature  under 
which  germination  is  most  rapid,  under  which  the  plants 
become  most  vigorous,  and  which  ensures  the  highest  per- 
centage of  plants  from  the  seed.     This  general  truth  should 
never  be  overlooked  in  the  spring  when  it  is  possible  to 
plant  in  a  too  cold  soil.     In  the  table  which  follows  are 


Soil  Temperatures. 


213 


given  the  best  soil  temperatures  and  the  lowest  and  high- 
est temperatures  at  which  certain  seeds  have  been  observed 
to  germinate. 


NAME  OF  PLANT. 

BEST  SOIL  TEMP. 

LOWEST  SOIL 
TEMP. 

HIGHEST  SOIL. 
TEMP. 

Sachs. 

Van 
Tiegham. 

Sachs. 

Van 
Tiegham. 

Sachs. 

Van 
Tiegham. 

Wheat  

84°  F. 
84 
84 
93 
79 
93 

81°  F. 
83 
80 
93 

41«F. 
41 

44.5 
48 
49 
54 

41"  F. 
41 
44 

49 

104°  F. 
104 
102 
115 
111 
115 

99°  F. 
100 

Barley  

115 

70 
89 
81 
99 

42 

82 
108 
99 

32 

The  two  important  facts  fixed  by  these  data  are:  (1) 
The  soil  temperatures  at  which  the  seeds  of  most  cultivated 
crops  germinate  best,  lie  between  70°  and  100°  F.,  with 
an  average  of  about  85°  F.  (2)  The  soil  temperatures 
below  which  germination  does  not  take  place  are  between 
41°  and  54°  F.  From  these  it  is  clear  that  seeding  should 
not  begin  until  the  thermometer  will  show  the  temperature 
of  the  soil  at  the  depth  of  planting,  well  up  toward  70° 
F.  during  the  warmest  portion  of  the  day.  These  state- 
ments should  not  be  understood  as  advising  against  the 
sowing  of  clover  seed  early  in  the  spring,  while  the  frost 
is  yet  on  the  ground,  under  conditions  where  it  might  not 
be  possible  to  get  a  stand  otherwise. 

256.  Observed  Soil  Temperatures — The  temperatures 
which  the  soil  does  attain  at  different  depths  during  the 
different  months  of  the  growing  season  will  be  of  inter- 
est in  connection  with  the  statements  made  in  the  last  two 
sections.  In  the  two  tables  which  follow  are  given  the 
mean  seasonal  variations  of  soil  temperature  at  two  sta- 
tions, one  in  this  country  and  the  other  in  Europe. 
14 


214 


Physics  of  the  Soil. 


Table  showing  the  mean  monthly  soil  temperatures,  at  State 
College,  Pa.,  by  Dr.  Frear,  and  at  Munich,  Germany,  by 
Ebermayer. 

AT  STATE  COLLEGE,  PENNSYLVANIA. 


Depth. 

April. 

May. 

June 

July. 

Aug. 

Sept. 

3  inches  

°F. 
43.74 

°F. 
55  13 

°F. 
67  29 

"F. 

70  16 

"F. 

68  70 

op 

01  32 

6  laches  

43  08 

5t  72 

63  34 

69.75 

68  49 

61  70 

12  inches  

42.69 

53  83 

65  03 

68  89 

68  66 

62.73 

24  inches  

41  43 

51  45 

61  90 

66  42 

67  41 

63  5'J 

AT  MUNICH,  GERMANY. 


44  65 

56  79 

61  11 

67  2ti 

61  09 

5S.21 

11.8  inches  
23  7  inches  

44.31 
44  40 

57.51 
53  58 

60.06 
59  11 

66.16 
63  12 

6.5  61 
63  55 

57.  S8 
58  82 

35.4  inches  

43.56 

51.24 

57.33 

62.92 

62.26 

ftfc.ol 

It  may  appear  that  the  temperatures  recorded  in  these 
tables  are  too  low  to  be  in  harmony  with  the  comparatively 
high  temperatures  given  as  the  best  for  germination.  It 
must  be  understood,  however,  that  the  average  must  bo 
lower  than  would  be  found  in  the  soil  during  the  warmest 
portion  of  the  day.  In  regard  to  the  minimum  tempera- 
ture at  which  germination  takes  place  it  will  be  clear 
enough  that  the  April  records  for  soil  temperature  are  quite 
in  harmony  with  those  given  for  germination. 

257.  Influence  of  Soil  Temperature  on  the  Rate  of  Germi- 
nation.— The  more  quickly  seeds  are  permitted  to  germi- 
nate after  they  are  placed  in  the  soil  the  higher  will  be 
the  per  cent,  of  seeds  growing  and,  as  a  rule,  the  more  vig- 
orous will  the  plants  be.  Indeed,  seeds  of  low  vitality 
placed  in  too  cold  a  soil  often  fail  to  germinate  at  all. 

Haberlandt  found  that,  when  corn  would  germinate  in 
3  days  at  a  temperature  of  65.3°  F.,  it  required  11  days 
when  the  soil  was  as  low  as  51°  F.,  and  Hellriegel  showed 
that  when  corn  was  planted  under  a  mean  temperature  of 
48°  only  2  out  of  10  kernels  sprouted  in  42  days;  that 
Vinder  the  same  temperature  rye  germinated  in  9  days, 


Conditions  Influencing  Soil  Temperatures.       215 

winter  wheat  in  12  days,  and  barley  and  oats  in  13  days, 
while  cucumbers  did  not  germinate  in  42  days. 

258.  Effect  of  Soil  Temperature  on  Root  Pressure. — The 

power  which  sends  the  soil  moisture  into  the  roots  of  plants 
and  up  into  the  leaves  is  osmotic  pressure,  developed  by 
the  warmth  of  the  soil,  and  unless  the  soil  temperature 
is  sufficiently  high  plants  may  wilt,  as  Sachs  has  shown, 
where  he  demonstrated  that  pumpkin  and  tobacco  plants 
wilted  badly,  even  at  night  with  an  abundance  of  moisture, 
as  soon  as  the  soil  temperature  fell  much  below  55°  F.,  the 
moisture  not  rising  fast  enough  to  compensate  for  even 
the  slow  evaporation  during  the  night. 

2C9.  Influence  of  Soil  Temperature  on  the  Formation  of 

Nitrates. — The  nitrates  in  the  soil  do  not  develop  until  the 
temperature  has  risen  above  41°  F. ;  the  action  of  the 
germs  is  extremely  feeble  at  54°  and  they  do  not  attain 
their  maximum  activity  until  a  soil  temperature  of  98°  has 
been  reached ;  but  if  the  earth  Becomes  as  warm  as  113°  F. 
then  the  action  is  nearly  stopped,  it  being  as  weak  as  at  54°. 


CONDITIONS     INFLUENCING     SOIL     TEMPEKATUKE. 

260.  Specific  Heat  of  Dry  Soil. — When  the  same  number 
of  heat  units  are  given  to  like  weights  of  different  kinds 
of  soil  their  temperatures  are  not  raised  through  the  same 
number  of  degrees  and  this  is  because  their  specific  heats 
(40)  are  different. 

From  the  determination  of  Oemler  it  appears  that  the 
number  of  heat  units  required  to  raise  the  temperature  of 
100  Ibs.  of  water  and  100  Ibs.  of  soil  of  different  kinds 
from  32°  to  33°  F.  is  as  stated  in  the  table  which  follows: 


216 


Physics  of  the  Soil. 


Table  of  specific  heat  of  dry  soils. 


No.  of  heat  units  re- 
quired to  raise  100  Ibs. 
from  32?  F.  to  33"  F. 

Temperature  of  100 
Ibs.  after  the  applica- 
tion of  100  heat  units. 

Water                

Heat  units. 
100  00 

•F. 
83  00 

22.15 

36.51 

20.86 

36  '79 

Sandy  humus  

14.14 

39  07 

16.62 

38  02 

Clayey  hum  us  

15.79 

38  53 

14.95 

38  68 

Pure  clay  

13.73 

39  28 

Sand  .        

10  08 

41  92 

18.48 

37  41 

It  is  clear  from  this  table  that  much  more  heat  is  re- 
quired to  raise  the  temperature  of  water  through  one  de- 
gree than  of  a  like  weight  of  dry  soil,  and  hence  that  a 
dry  soil  will  warm  in  the  sunshine  more  rapidly  than  a 
moist  soil  can. 

261.  Specific  Heat  of  Wet  Soil. — The  differences  m  the 
weight  per  cubic  foot  of  dry  soils  and  the  differences  in 
their  water  content  greatly  affect  the  specific  heat  or  the 
rate  at  which  the  surface  temperatures  will  rise  under  the 
same  conditions. 

Sand  has  a  small  capacity  for  water  and  on  this  account 
is  naturally  warm,  but  its  greater  weight  per  cubic  foot 
acts  as  an  offset,  tending  to  make  it  colder.  If  a  loosely 
packed  clay  loam  weighs  70  Ibs.  per  cubic  foot  and  a 
sandy  soil  106  Ibs.  and  the  two  hold  33  per  cent,  and  18 
per  cent,  of  water  respectively,  when  capillarily  satur- 
ated, then  the  number  of  degrees  F.  that  100  heat  units 
will  raise  the  temperature  of  a  cubic  foot  of  each  soil  when 
saturated,  half  saturated  and  dry  are  given  below: 


Saturated. 

Half  saturated. 

Dry. 

Sandy  soil  

3  4°F. 

5.°F. 

9.92°  F. 

2.98 

4.49 

6  02 

.42 

.51 

3.9 

Conditions  Influencing  Soil  Temperatures.       217 

One  thousand  heat  units  would  raise  the  differences  in 
temperatures  to  4.2°,  5.1°  and  39°,  making  it  clear  that 
the  differences  in  weight  and  in  water  content  greatly  in- 
fluence the  degree  of  warmth. 

262.  Influence  of  Color  on  Soil  Temperature. — The  color 
of  a  soil,  especially  when  dry,  so  that  the  rate  of  evapora- 
iton  from  its  surface  is  small,  has  a  marked  influence  on 
the  temperature,  even  at  considerable  depths.  Wollny 
made  a  series  of  experiments  to  note  the  effect  of  color, 
using  white  marble  dust  and  lampblack  in  different  pro- 
portions, to  secure  different  shades  from  light  grey  to  black, 
in  which  he  placed  two  thermometers,  one  with  the  bulb 
just  beneath  the  surface  and  the  other  4  inches  below.  The 
temperatures  were  taken  every  two  hours  of  the  24  and 
the  results  are  given  in  the  table  below,  together  with  those 
of  a  similar  trial  using  yellow  ocher. 

Table  showing  the  influence  of  color  on  the  temperature  of  soil. 


AT  THE  StJBFACB. 

AT  FOUB  INCHES  DBEP. 

Black. 

Dark 
grey. 

Med'm 
grey. 

Light 
grey. 

Black. 

Dark 

grey. 

Med'm 
grey. 

Light 
grey. 

Mean  temp.. 
Variations... 

"P. 
32.82 
31.55 

«P. 
32  39 
32.90 

31.98 
32.45 

°T7 

30.94 
30.10 

°F. 
28.33 
15.20 

28.46 
14.25 

oF 

27.  83 
12.50 

"F. 
27.20 
11.85 

Dark 
brown. 

Medium 
brown. 

Light 
brown. 

Faint 
brown. 

Dark 
brown. 

Medium 
brown. 

Light 
brown. 

Faint 
brown. 

Mean  temp 
Variations    . 

°F. 
31.76 
81.95 

•F. 
81.65 
31.75 

°F. 
30.93 
29.90 

°F. 
30.70 
27.65 

WF. 
27.29 
12.30 

27.19 
12.15 

27.34 
11.  iO 

•F, 

ST.  40 
10.75 

From  this  table  it  appears  that  the  darkest  soil,  whether 
black  or  brown,  was  more  than  a  degree  warmer  than  the 
light  soil  at  four  inches  deep ;  and  that  the  black  soil  had 
a  daily  variation  in  temperature  at  four  inches  more  than 
3°  F.  greater  than  the  light  soil,  and  the  dark  brown  soil 
one  of  1.55°  F. 


218 


Physics  of  the  Soil. 


263.  Influence  of  Topography  on  Soil  Temperature. — The 
degree  of  inclination  of  the  land  surface  and  the  direction 
of  the  slope,  whether  facing  east,  west,  north  or  south,  may 
exert  a  marked  influence  upon  the  temperature  of  the  soil 
and  particularly  upon  its  diurnal  range.  The  tempera- 
ture of  a  stiff  red  clay  soil,  upon  a  level  table,  and  upon  a 
south  exposure  sloping  about  18°,  was  found  in  the  sur- 
face three  feet  to  be  as  represent  CM!  in  the  table  below : 

Showing  the  influence  of  topography  upon  soil  temperature. 


KIND  OF  SOIL. 

DEPTH  BELOW  THE  SURFACE. 

1st  foot. 

2nd  foot.         3rd  foot. 

Red  clay, 
Red  clay, 

south  slope  

70.  3°  F. 
C7.2 

3.1 

68.1°F. 
65.4 

2.7 

66.4°  F. 
63.6 

2.8 

level  surface  

,  Here  it  is  seen  that  the  effect  of  a  south  exposure  is  to 
make  a  difference  in  temperature  of  from  a  little  more  than 
3°  F.,  in  the  surface  foot,  to  a  little  less  in  the  second  and 
third  feet. 

The  reason  for  these  differences  will  be  readily  under- 
stood from  a  study  of  Fig.  61.  Suppose  A  6  5  Bte  rep- 
resent a  section  of  a  prism 
of  sunshine  falling  upon 
the  hill  A  E  B,  where  A  E 
is  the  south  slope  and  .E  B 
is  the  north.  On  account 
of  the  sun  not  being  di- 
rectly vertical  over  the  hill 
the  south  slope  receives  as 
.,  much  more  heat  in  a  unit 

FIG.  61.— Influence  of  topography  on  soil      ,  T.I 

temperature.  oi    time    than    the    nortn 

elope  as  the  line  4-6  is  longer  than  the  line  4-5. 


264.  Influence  of  Looseness  and  TJnevenness  of  Surface  on 
Soil  Temperature. — When  a  field  is  left  very  uneven,  and 


Conditions  Influencing  Soil  Temperatures.       219 

especially  if  covered  with  lumps,  the  large  amount  of  sur- 
face exposed  to  the  sky  and  to  the  air  permits  the  heat  of 
the  surface  soil  to  be  lost  rapidly  in  warming  the  air  above 
and  the  result  is  the  deeper  soil  remains  at  a  lower  tem- 
perature. So,  too,  if  the  soil  is  loose  and  open,  the  dry 
superficial  layer  becomes  warm  and  heats  the  air,  while 
the  poor  conducting  capacity  of  the  open  soil  prevents  the 
heat  from  being  conveyed  deeply  below  the  surface  and  a 
lower  temperature  is  the  result. 

265.  Influence  of  Surface  Tillage  on  Soil  Temperature. — 
When  corn  rround  was  cultivated  3  inches  deep  as  com- 
pared with  1.5,  in  alternate  groups  of  four  rows,  the  mean 
temperatures  of  the  soil  ifi  the  first,  second  and  third  feet 
below  the  soil  stirred  was  found  to  be  .82°  F.  warmer  in 
the  first  foot  and  .59°  F.,  and  .36°  F.  respectively  in  the 
second  and  third  feet  on  the  ground  receiving  the  shallower 
cultivation. 

266.  Influence  of  Chemical  and  Physical  Changes  on  Soil 
Temperature. — When  heavy  dressings  of  farmyard  manure 
are  plowed  in,  and  when  heavy  crops  are  turned  under  for 
green  manure,  the  fermentation  which  is  set  up  in  these 
materials  results  in  a  measure  of  heat  which  warms  the 
soil  in  the  same  way  that  a  manure  heap  heats  when  fer- 
menting.    Indeed  all  of  the  steps  in  the  formation  of  ni- 
trates in  the  soil  result  in  the  evolution  of  some  heat. 

Again,  when  the  surfaces  of  dry  soil  grains  become  mois- 
tened with  %vater,  whether  by  "rain  or  by  capillary  move- 
ments, surface  tension  in  forcing  the  water  to  surround 
the  soil  grains  generates  a  small  amount  of  heat,  which 
affects,  in  so  far,  the  soil  temperature. 

267.  Influence   of  Rains   on   Soil   Temperature. — Heavy 
rains  which  fall  upon  fields  and  penetrate  the  soil  may  ex- 
ert very  marked  effects  upon  its  temperature  on  account  of 
the  relatively  high  specific  heat  of  the  water  as  compared 
with  that  of  the  soil. 

If  the  atmosphere  is  wanner  than  the  deeper  soil,  as 


220 


Physics  of  the  Soil. 


may  be  the  case  in  the  spring,  and  if  rains  fall  which  re- 
sult in  heavy  percolation,  a  large  amount  of  heat  is  con- 
veyed rapidly  and  deeply  into  the  soil  with  the  water  and 
the  temperature  of  the  ground,  two  to  four  feet  below  the 
surface,  may  thus  be  very  materially  raised. 

268.  Influence  of  Evaporation  on  Soil  Temperature. — 
There  is  no  factor,  except  the  direct  sunshine  and  the  direct 
radiation  of  heat  away  from  the  earth  into  space,  which 
exerts  so  strong  an  influence  on  the  temperature  of  the  soil 
as  the  evaporation  of  moisture  from  its  surface;  and  the 
chief  reason  why  an  undrained  clay  soil  is  colder  than  ono 
well  drained  is  the  cooling  effect  associated  with  the  larger 
evaporation  of  soil  moisture. 

To  evaporate  a  pound  of  water  from  the  surface  of  a 
square  foot  of  soil,  by  means  of  the  heat  contained  in  the 
soil,  makes  it  imperative  that  966.6  heat  units  be  expended 
to  do  the  work  and  this,  if  withdrawn  from  a  cubic  foot  of 
saturated  clay  soil,  would  lower  its  temperature  some 
10.3°  F. 

The  difference  in  temperature  shown  by  the  wet  and  dry 
bulb  thermometers  measures,  in  one  way,  the  cooling  effect 
of  evaporation ;  the  wet  bulb  often  reading  as  much  as  15 
or  even  20  degrees  lower  than  the  dry  one,  under  otherwise 
identical  conditions. 

Table  showing  the  influence  of  rapid  evaporation  upon  the 
temperature  of  the  soil. 


Date. 

Time. 

Condition  of 
weather. 

Temp, 
of  air. 

Temp,  of 
drained 

soil. 

Temp, 
of  un- 
drained 
soil. 

Differ- 
ence. 

April  24^ 

3.  30  to 
4pm. 

Cloudy,  with  brisk 
east  wind. 

5j£ 

|eo.5 

QJJI 

66.5 

°F. 
54  00 

"F. 

12.50 

April  25J 

3  to  3.30 

p.  in. 

Cloady,   with  brisk 
east  wind. 

'-64.0 

70.0 

58.00 

12.03 

April  26] 

1.30  to 
2  p.  m. 

Cloudy,  rain  all  the 
forenoon. 

[45.0 

50.0 

44.00 

6.00 

April  27] 

l.POto 
2  p.  m. 

Cloudy  and  sunshine, 
wind  S.  W.  brisk. 

^530 

55.0 

50.75 

4.23 

April  2SJ 

7  to  8.SO 
a.  m. 

Cloudy  and  sunshine, 
wind  N.  W.  brisk. 

[45.0 

47.0 

44.50 

2.50 

.    Means  of  Controlling  Soil  Temperature.         221 

In  the  table  above  are  given  the  observed  differences 
in  temperature  of  a  well  drained  sandy  loam  and  an  ad- 
jacent black  marsh  soil,  not  well  drained,  the  observa- 
tions being  taken  simultaneously  and  the  differences  in 
temperature  being  due  largely  to  differences  in  the  rate  of 
evaporation  in  the  two  cases. 

MEANS  OF  CONTROLLING  SOIL  TEMPERATURE. 

269.  Effect  of  Rolling  on  Soil  Temperature. — In  the  spring 
of  the  year,  when  the  soil  is  naturally  cold,  the  first  effect 
of  rolling  is  to  cause  the  soil  to  warm  deeply  at  a  more 
rapid  rate,  and  Fig.  62  shows  how  strong  this  influence 
may  be.  In  extreme  cases  the  soil  temperature,  at  1.5 
inches  below  the  surface,  has  been  found  as  much  as  10°  F. 
higher  than  on  entirely  similar  and  adjacent  ground,  not 
rolled,  and  6.5°  at  3  inches  below  the  surface.  This  dif- 
ference is  due  to  the  better  conducting  power  of  the  soil, 
on  account  of  its  firmer  texture,  and  is  in  spite  of  the  loss 
of  heat  due  to  greater  evaporation  which  takes  place  from 
the  rolled  surface. 


FIG.  62.— Showing  the  effect  of  rolling  on  soil  temperature. 

The  average  difference  in  temperature  of  soil  on  eight 
Wisconsin  farms,  at  the  season  when  oats  were  germinat- 
ing, was  found  to  be  as  given  in  the  table  below: 


222 


Physics  of  the  Soil. 


Time. 

Mean  air 
temp. 

Mean  soil  temperature  at 
1.5  inches  deep. 

Mean  soil  temperature  at 
3  inches  deep. 

' 
2  to  4  p.  in... 

65.37°  F. 

Rolled. 
71.69°F. 

Unrolled. 
68.57°F. 

Rolled. 
67.33T. 

Unrolled. 
64.39"  F- 

Here  is  a  mean  difference  of  3.1°  I\  at  1.5  inches,  arid 
2.9°  F.  at  3  inches  deep  in  favor  of  the  rolled  surface. 

270.  Influence  of  Thorough  Preparation  of  the  Seed-bed  on 
Soil  Temperature. — It  follows,  from  what  has  been  said  in 
previous  paragraphs,  that  the  practice  of  thoroughly  pre- 
paring the  seed-bed  before  sowing  or  planting  must  have 
the  effect  of  decreasing  the  capillary  rise  of  cold  water 
from  below  and  its  loss  by  evaporation  from  the  soil.     This 
then  would  tend  to  concentrate  the  sun's  heat  in  the  seed- 
bed itself,  first  by  lessening  its  rate  of  conduction  down- 
ward, and  second  by  diminishing  its  loss,  by  lessening  the 
evaporation.       In  the  spring,    then,  early  and    thorough 
preparation  of  the    seed-bed  tends    to  make    the  seed-bed 
warmer ;  it  diminishes  the  loss  of  soil  moisture ;  it  increases 
the  formation  of  nitrates,  thus  making  the  soil  richer;  it 
hastens  and  makes  stronger  the  germination  and  it  enables 
one  or  more  crops  of  weeds  to  be  destroyed  before  the  crop 
is  up  in  the  way  of  cultivation.     Hence  there  is  much  to 
gain  and  little  to  lose  in  the  thorough  preparation  of  tho 
seed-bed  before  planting. 

271.  Controlling  Soil  Temperature  by  TTnderdraining. — 
When  land  naturally  too  wet  for  tillage  early  in  the  spring 
has  been  thoroughly  underdrained,  the  soil  is  brought  into 
fit  condition  for  seeding  much  earlier  than  would  be  pos- 
sible without  this  improvement,  and  one  of  the  great  points 
gained  is  the  warming  of  the  soil  to  a  greater  depth,  on 
account  of  the  removal  of  the  water  and  tlie  lessening  of 
the  loss  of  heat  by  evaporation. 


CHAPTER  XL 


OBJECTS,   METHODS  AND   IMPLEMENTS   OF   TILLAGE. 

Tilling  the  soil  is  one  of  the  oldest  of  agricultural  arts, 
and  during  its  long  practice  very  many  methods  have  been 
adopted  and  tools  devised  for  securing  the  ends  sought. 

272.  Objects  of  Tillage. — The  term  "tillage"  has  been 
applied  to  the  different  methods  of  working  the  soil  in  or- 
der to  secure  the  conditions  needful  for  the  growth  of  cul- 
tivated crops.  The  chief  objects  which  tillage  aims  to 
secure  are: 

1.  To   destroy   and   prevent  the  growth  of  weeds  and 
other  vegetation  not  desired  upon  the  ground. 

2.  To  place  beneath  the  surface  manure,  stubble  and 
other  organic  matter  where  it  will  not  be  in  the  way  and 
where  it  may  be  converted  rapidly  into  humus. 

3.  To  develop  various  degrees  of  openness  of  texture 
and  uniformity  of  soil  conditions  suitable  to  the  planting 
of  seeds  and  the  setting  of  plants. 

4.  In  still  other  cases  the  object  of  tillage  may  be  to  so 
modify  the  movements  of  soil  moisture  and  of  soil  air. 

5.  In  still  other  cases  the  objects  of  tillage  may  be  to  so 
chang'e  conditions  as  to  make  the  soil  either  warmer  or 
colder. 


TILLAGE  TO  DESTROY  WEEDS. 

It  must  ever  be  kept  in  mind  that  wherever  weeds  are  al- 
lowed to  grow  they  are  removing  from  the  soil  both  avail- 
able moisture  and  plant  food  in  the  form  of  soluble  salts 
and,  to  whatever  extent  this  is  permitted,  to  that  extent  is 


224:  Physics  of  the  Soil. 

the  possible  yield  of  any  crop  lessened.  No  soil  can  mature 
a  maximum  crop  of  corn  when  weeds  are  permitted  to  grow 
with  it.  Neither  is  it  possible  for  an  orchard  of  any  kind  to 
come  into  hearing  as  quickly  or  to  produce  as  vigorous 
trees  where  the  soil  between  and  beneath  them  is  occupied 
by  either  weeds  or  grass.  It  may  be  thought  that  so  long  as 
the  weeds  are  destroyed  upon  the  ground  they  return  to  it 
whatever  they  have  taken  out  and  therefore  cannot  leave 
the  soil  poorer.  To  this  it  must  be  said  that  whatever 
moisture  is  removed  is  a  positive  loss  because  it  is  carried 
away  by  the  winds;  the  nitric  acid  that  is  taken  up  and  the 
potash,  phosphoric  acid  and  other  ash  ingredients  are  also 
largely  a  positive  loss  so  far  as  that  season  is  concerned  for 
they  are  removed  from  the  soil  moisture  and  converted  into 
dry  matter  in  the  tissues  of  the  weeds  where  the  crop  can- 
not use  them.  Even  if  the  weeds  are  killed  while  the  crop 
is  yet  on  the  ground  they  cannot  furnish  food  for  it  for 
they  are  likely  not  to  decay  soon  enough  to  become  at  once 
available. 

273.  The  Best  Time  to  Kill  Weeds. — The  best  time  to  kill 
weeds  is  just  as  the  seeds  are  germinating  or  while  they 
are  yet  very  small.  When  this  is  done  but  little  moisture 
is  lost  through  them  and  they  render  but  little  plant  food 
insoluble.  In  the  thorough  and  early  preparation  of  the 
seed-bed  many  weeds  are  destroyed  by  killing  them  just  as 
they  are  coming  up.  So,  too,  in  the  case  of  a  grain  field, 
which  is  rolled  after  being  seeded  and  is  then  harrowed,  the 
rolling  hastens  the  germination  of  the  weed  seeds  and  the 
harrowing  then  throws  them  out  into  a  dry  soil  which  kills 
them.  If  such  a  field  is  again  harrowed  just  after  the  grain 
is  up  a  second  crop  of  weeds  may  be  destroyed  and  the 
yield  made  greater  as  a  consequence. 

In  the  case  of  potatoes  and  corn  it  is  very  easy  to  destroy 
at  least  two  crops  of  weeds  before  the  corn  or  potatoes  are 
large  enough  to  cultivate,  by  harrowing  before  and  just 
after  the  plants  are  up.  This  is  very  important  because  it 
not  only  saves  plant  food  for  the  crop  but  it  can  be  done 


Tillage  to  Destroy  Weeds.  225 

so  much,  more  cheaply  and  rapidly  with  the  broad  light 
harrows  and  weeders  than  it  can  later  with  the  cultivator. 

274.  Weed  Seeds  Do  not  All  Germinate  at  Once — It  must 
be  remembered  in  handling  soils  to  kill  weeds  that  the  seeds 
do  not  all  germinate  at  once.  The  first  harrowing  which  is 
done  to  kill  weeds  may  itself  bring  up  from  below  seeda 
whioh  were  too  deep  in  the  ground  to  grow  or  it  may  cover 
some  seeds  which  were  lying  upon  or  too  close  to  the  sur- 
face to  germinate,  hence  frequent  cultivations  for  hoed 
crops  are  needful. 

275.  The  Best  Tools  for  Weed  Killing. — The  tool  which 
will  do  the  most  effective  service  in  killing  weeds  depends 
upon  the  character  and  condition  of  the  soil  and  the  size  of 
the  weeds.    When  they  are  not  yet  fairly  out  of  the  ground 
or  are  just  coming  up  and  before  a  root  system  has  been  de 
veloped  there  is  no  tool  equal  to  a  medium  weight  or  light 
spike-toothed  harrow  represented  in  Fig.  6  2  a.     The  stiffer 
and  more  compact  the  soil  is  the  heavier  should  be  the  har- 
row or  rather  the  deeper  it  should  be  run  in  the  ground. 


FIG.  62a.— Tilting  harrow,  best  tool  for  killing  young  weeds. 

The  tilting  harrow,  constructed  so  that  the  teeth  may  be 
inclined  forward  or  backward,  is  one  of  the  best  forms  a?, 
with  this  arrangement,  it  may  be  made  to  run  deep  or  shal- 
low as  desired. 

On  sandy  soils  and  other  soils  when  very  loose  the  form 
of  tool  represented  in  Fig.  63  may  be  used  to  kill  very 


226 


Physics  of  the  Soil. 


young  weeds  before  they  are  well  rooted ;  but  this  is  not  an 
effective  tool  when  weeds  have  a  start  nor  where  the  soil  is 
at  all  hard  or  heavy. 


FIG.  63.— Weeder. 


276.  Cultivation    After    the    Harrowing    Stage. — When 
plants  have  become  too  large  to  permit  the   harrow  or 
weeder  to  be  used  to  advantage  a  tool  with  broader  teeth  is 
needed.     Cultivation  or  intertillage  should  begin  as  soon 
as  the  first  fresh  weeds  start  and  great  pains  should  be 
taken  to  work  so  close  to  the  row  that  all  the  soil  is  either 
stirred  or  covered  with  a  thin  layer  of  fresh  soil.     Few 
realize  how  close  it  is  possible  to  work  to  a  row  without 
either  covering  the  plants  or  seriously  injuring  the  roots, 
until  they  have  learned  to  do  it.     It  is  early  and  frequent 
harrowing  and  careful  close  first  cultivation  that  insures 
scrupulously  clean  fields  and  the  largest  yields  the  season's 
rainfall  will  permit. 

277.  Cultivators  for  Intertillage.— When  harrowing  has 
been  properly  practiced  intertillage  may  begin  with  a  tool 
\vhose  teeth  are  about  2  inches  wide  and  there  should  be 
enough  of  them  to  thoroughly  stir  the  whole  soil  surface  to 
a  depth  of  two  and  one-half  to  three  inches.    Fig.  64  shows 
a  good  set  of  teeth  for  soils  not  too  heavy,  while  Fig.  65 
shows  a  tool  which  should  not  as  a  rule  find  a  place  in  well 
cared  for  fields,  for  the  teeth  are  too  wide  and  too  few  for 
good  general  work.  They  are  wasteful  of  moisture,  waste- 
ful of  fertility  and  liable  to  do  too  much  root  pruning. 


Tillage  to  Destroy  Weeds. 


22^ 


FIG.  64.— A  type  of  good  cultivator. 

Cultivators  with  rigid  teeth  like  those  of  Fig.  66  do  bet- 
ter work  as  a  rule  than  those  of  the  spring  tooth  type  rep 
resented  in  Fig.  64,  for  the  reason  that  the  ground  is 
stirred  more  completely  and  to  a  more  uniform  depth.  On 
naturally  mellow  soils  the  spring  tooth  is  good  and  where 
the  land  is  very  stony  it  is  safer  against  breaking. 


FIG.  65. — Cultivator  with  too  wide  teeth  for  general  use. 


228 


Physics  of  the  Soil. 


278.  Easy  and  Quick  Movement  of  Teeth. — A  very  im- 
portant feature  of  a  riding  or  walking  sulky  cultivator  is  to 
have  the  gangs  of  teeth  so  swung  from  the  carriage  that  a 
slight  effort  will  produce  a  quick  and  certain  movement. 
This  is  indispensable  in  order  to  work  close  to  the  rows. 


FIG.  66.— Cultivator  with  rigid  teeth;  best  where  soil   is  heavy  and  not 

stony. 

279.  The  Teeth  of  the  Cultivator  Adjustable. — Another 
important  feature  sulky  cultivators  should  possess  is  the 
possibility  of  tilting  the  gangs  so  as  to  allow  them  to  work 
more  deeply  in  the  soil  toward  the  center  of  the  row  in  the 
later  stages  of  cultivation  because  then  the  roots  near  the 
rows  have  developed  close  to  the  surface,  and  deeper  culti- 
vation in  the  center,  where  the  soil  is  more  exposed  to  the 
sun,  is  needed  for  effectiveness  as  a  mulch. 


280.  Covering  Weeds  in  the  Row. — It  sometimes  happens 
with  the  most  careful  management  that  weeds  will  get  such 
a  start  in  the  row  that  either  hand  hoeing  must  be  resorted 
to  or  else  a  tool  must  be  used  which  will  throw  enough 


Tillage  to  Destroy  Weeds.  229 


JANESVlLLE    TDISK      CULTIVATOR  *' 


FIG.  67.— Cultivator  which  can  be  used  to  cover  weeds  in  row. 


15 


FIG.  68.— Tool  for  shallow  surface  cultivation. 


230 


Physics  of  the  Soil. 


earth  to  cover  the  weeds  in  the  row.  A  good  cultivator  for 
this  kind  of  work  is  represented  in  Fig.  67.  The  levelers 
represented  in  the  rear  of  the  discs  are  intended  to  throw 


FIG.  69.— Two  good  garden  cultivators. 

the  earth  back  to  prevent  ridging  when  the  tool  is  used  for 
ordinary  cultivation  and  ridging  is  not  desired. 

281.  Garden  Cultivators. — Two  good  forms  of  garden  cul- 
tivators are  represented  in  Fig.  69,  where  the  upper  one  is 
to  be  used  early,  when  the  plants  and  weeds  are  small,  and 
the  lower  one  when  the  harrow-stage  has  passed.  In  the 
garden  as  in  the  field  the  best  time  to  kill  weeds  is  just  aa 


Tillage  to  Modify  Soil  Texture. 


231 


the  seeds  are  germinating  and  emerging  from  the  soil  and 
the  harrow-soothed  cultivator  is  very  effective  in  doing  this. 
It  stirs  the  surface  thoroughly  enough  to  throw  the  young 
weeds  out  and  cause  the  soil  close  to  the  surface  to  dry 
sufficiently  to  kill  them.  Much  worry  and  hard  work  will 
be  saved  by  the  timely  use  of  this  or  a  similar  tool. 


TILLAGE  TO  MODIFY  SOIL  TEXTUEE. 

282.  Soil  Texture  and  Tilth. — Texture  of  soil,  like  the 
texture  of  cloth  has  reference  to  the  size  of  the  elements 
which  give  it  its  evident  structure;  and  just  as  the  threads 
of  a  piece  of  cotton,  a  piece  of  woolen  or  a  piece  of  silk  are 


FIG.   70.— Showing  the  granular  character  of  a  soil   in  good  tilth  after 

cultivation. 

made  by  twisting  together  varying  numbers  of  small  fibers, 
making  the  threads  coarse  or  fine,  so  is  it  with  soils ;  they 
are  composed  of  granules  of  varying  sizes  formed  out  of 
ultimate  soil  grains  which  are  cemented  together  more  or 


232  Physics  of  the  Soil. 

less  firmly.  Fig.  70  represents  the  textural  elements  of  a 
clay  loam  in  pretty  good  tilth.  There  are  shown  seven 
sizes  of  granules  large  enough  to  be  readily  distinguished 
with  the  naked  eye,  and  each  size  is  composed  of  fine  soil 
grains  cemented  together.  All  are  represented  natural 
size  and  were  carefully  drawn  from  an  actual  sample  taken 
from  a  three  inch  mulch  as  left  after  the  cultivator. 

The  granules  were  sorted  by  means  of  a  series  of  sieves 
and  the  relative  amount  of  each  size  of  granules  is  repre- 
sented by  the  shading  in  the  vials  where  it  is  seen  that  the 
largest  size  constitutes  the  smallest  part  of  this  soil,  and 
No.  5  the  largest  portion.  The  finest  grade,  No.  8,  is  also 
largely  composed  of  compound  grains,  many  large  enough 
to  be  clearly  distinguished  by  the  unaided  eye,  but  many 
more  of  the  ultimate  grains  which  were  rubbed  off  from 
the  larger  grains  by  cultivating  and  during  the  process  of 
screening. 

Just  as  woolen  cloths  differ  when  the  threads  are 
of  the  same  size  because  some  are  twisted  from  finer  and 
others  from  coarser  wool,  so  soils  differ  in  having  their 
granules  made  of  coarser  or  finer  soil  particles  cemented 
together. 

Then,  too,  just  as  one  cloth  may  differ  from  another  in 
having  its  threads  loosely  twisted^  while  another  is  hard 
twisted,  so  one  soil  may  differ  from  another  in  the  degree  of 
firmness  with  which  the  soil  particles  are  cemented  to- 
gether. 

Still  again,  just  as  one  fabric  may  be  loosely  woven 
while  another  is  firm,  so  one  soil  may  have  its  granules  more 
strongly  cemented  together  than  another,  making  it  hard  to 
work  and  heavy  while  the  other  is  light  and  mellow. 

A  sand  differs  from  a  soil  in  being  composed  of  simple 
separate  grains,  usually  of  rather  large  size,  while  a  clay  is 
composed  very  largely  of  extremely  fine  granules  made 
from  the  finest  of  particles. 

A  soil  is  in  good  tilth  when  its  granules  are  neither  too 
fine  nor  too  coarse,  and  when  they  are  not  too  firmly 
cemented  together. 


Tillage  to  Modify  Soil  Texture.  233 

283.  Why  Good  Tilth  and  Good  Tillage  Are  Important — 
It  is  clear  from  the  rounded  form  of  the  granules  of  soil 
shown  in  Fig.  70,  that  when  they  are  massed  together  with- 
out being  crushed  a  very  large  amount  of  unoccupied  space 
must  exist ;  this  unoccupied  space  in  a  soil  is  needed  for  the 
movement  of  air  and  of  water;  for  the  spreading  out  of 
the  root  fibers  and  root  hairs,  and  for  the  home  of  micro- 
organisms which  develop  the  available  nitrogen  used  by  all 
the  higher  plants. 

If  the  granules  are  too  large  and  too  loosely  packed  the 
soil  lets  the  rains  fall  through  it  too  freely  and  does  not 
bring  it  back  rapidly  enough  by  capillarity  to  meet  the 
needs  of  crops.  If  the  granules  are  too  small  and  too  close 
then  the  water  moves  too  slowly,  too  much  is  retained  by 
capillarity  and  there  is  too  little  air.  If  the  granules  are 
bound  together  too  strongly,  the  soil  is  too  hard  and  the 
roots  are  unable  to  set  it  aside  in  making  their  advance  and 
this  lack  of  freedom  reduces  the  yield. 

284.  How  Texture  and   Tilth  Are   Developed. — The   soil 
particles  are  drawn  together  into  the  rounded  granules  by 
the  tension  of  the  soil  water  in  the  same  way  that  water 
forms  itself  into  spheres  when  sprinkled  on  a  dust  covered 
floor.    As  long  as  there  are  large  open  spaces  in  the  soil  not 
filled  with  water  the  water  is  all  the  time  drawing  itself  to- 
gether, tending  to  form  spheres,  and  in  this  system  of  pulls 
the  soil  particles  become  involved  and  are  drawn  together 
also.     As  the  water  is  lost  by  evaporation  and  the  salts  dis- 
solved become  too  strong  to  remain  in  solution  they  are  de- 
posited upon  and  between  the  grains  and  granules  tending 
to  cement  them  together. 

285.  Difference  Between  Soil  and  Potter's  Clay. — When 
the  granules  of  a  fine  soil  are  all  broken  down  and  separated 
into  their  ultimate  grains  we  have  the  puddled  condition  so 
fatal  to  crops,  but  the  one  the  potter  strives  to  secure  to 
make  his  wares  close  in  texture  and  strong.     In  the  pud- 
dled soil  and  potter's  clay  enough  of  the  granules  have  been 


234 


Physics  of  the  Soil. 


broken  down  to  fill  the  spaces  between  the  larger  simple 
grains  and  finer  granules  not  yet  broken  down  to  make  a 
close  textured,  impervious  material  in  which  no  plant  can 
thrive,  and  through  which  neither  water  nor  air  can  move. 

286.  Early  Spring  Tillage — The  early  stirring  of  the  soil 
in  the  spring  preparatory  to  seeding  has  for  its  main  object 
the  changing  of  the  soil  "texture  so  that  it  will  become  1st, 
warmer,  2d,  dryer,  3d,  better  aerated,  4th,  better  suited  to 
lessen  the  rate  of  evaporation  of  the  deeper  soil  water,  and 
5th,  to  hasten  the  development  of  weed  seeds  so  they  may 
be  destroyed  before  the  crop  is  in  the  way  of  killing  them. 


mj  iS 


FIG.  71.— The  disc  harrow. 


287.  The  Disc  Harrow.— One  of  the  best  tillage  tools  yet 
devised  is  the  disc  harrow  represented  in  Fig.  71.  There 
is  no  harrow  which  so  thoroughly  pulverizes  a  soil  in  the 
spring  after  fall  plowing  as  this  tool.  When  set  to  work 
deep  the  draft  is  heavy  but  the  amount  of  work  it  is  doing 


Tillage  to  Modify  Soil  Texture. 


235 


is  relatively  large.  To  put  a  piece  of  fall  plowing  in  the 
best  shape  the  harrow  should  be  lapped  half  and  in  doing 
this  the  furrow  between  the  two  sets  of  discs  will  be  en- 
tirely filled  and  the  surface  left  level. 


FIG.   72.— Spring-tooth  harrow. 

Where  small  grains  are  to  follow  corn  or  potatoes  the  use 
of  this  tool  will  often  make  the  plow  unnecessary. 

On  the  upland  prairie  soils  and  others  naturally  mellow, 
ground  for  corn  njay  be  plowed  in  the  fall  and  fitted  in  the 
spring  with  the  disc  harrow  with  good  results. 

288.  The  Spring  Tooth  Harrow. — On  new  land  in  wooded 
countries  and  where  the  fields  are  rough  and  stony  the  har- 


FIG.  73.— Spike-tooth  or  smoothing  harrow. 


236  Physics  of  the  Soil. 

row  represented  in  Fig.  72  does  good  work.  Its  weight 
forces  it  into  the  soil  and  the  elasticity  of  the  teeth  prevent 
them  from  being  broken,  but  such  tools  can  never  do  the 
degree  of  pulverizing  that  the  disc  harrow  accomplishes. 

289.  Smoothing  Harrows — When  the  soil  has  been  pul- 
verized with  the  disc  or  other  tool  and  it  is  desired  to  leave 
the  surface  more  nearly  even,  or  where  the  soil  is  naturally 
very  mellow,  making  less  force  necessary  to  change  the 
surface  texture,  then  the  heavier  weights  of  tilting  har- 
rows, Fig.  73,  may  be  used  to  great  advantage  on  account 
of  the  greater  area  which  may  be  covered  with  them  in  a 
day  and  their  lighter  draft. 


FIG.  74.— The  planker. 


290.  The  Planker. — It  is  sometimes  desirable  to  leave  the 
surface  particularly  smooth  without  firming  it  and  at  the 
same  time  to  crush  lumps.    This  may  be  done  by  means  of 
a  planker  made   of   three   to   five   8-  or    10-inch   plank 
bolted  together  with  their  edges  overlapping  as  represented 
in  Fig.  74.     The  tool  is  best  made  of  oak  plank  two  inches 
thick  and  eight  to  twelve  feet  long.     Such  a  tool  cannot 
take  the  place  of  a  roller  where  it  is  desired  to  firm  the 
ground. 

291.  The  Use  of  the  Roller — The  roller  is  used  chiefly 
when  it  is  desired  to  firm  the  surf  ace  and  to  help  cover  seed, 
especially  when  sown  broadcast.     In  other  cases  it  may  be 
used  to  crush  clods  or  to  compress  the  furrow  slices  after 
the  sod  plow.    Again  when  a  green  crop  like  rye  or  clover 
has  been  turned  under  for  manure,  or  where  coarse  litter 
has  been  plowed  under,  a  roller  is  needed  to  compress  the 
soil  and  establish  good  capillary  connection  with  the  deeper 
Boil  water.    It  is  sometimes  used  to  develop  a  mulch  where 
grain  is  rolled  after  it  is  up. 


Tillage  to  Modify  Soil  Texture. 


237 


In  all  of  these  cases  weight  is  one  of  the  essential  feat- 
ures of  the  tool.  A  roller  for  tillage  should  have  a  weight 
of  about  100  Ibs.  to  the  running  foot  and  a  diameter  of 
about  2  feet. 


FIG.  75.— Two  types  of  rollers. 

Two  types  of  rollers  are  represented  in  Fig.  75,  the  one 
made  of  bars  being  designed  to  crush  clods  more  completely 
and  to  leave  the  surface  ridged  so  as  to  be  less  likely  to  be 
influenced  by  the  wind  drifting  the  surface  soil. 

292.  The  Harrow   Should   Follow   the  Roller. — In   most 

cases  when  it  has  been  desirable  to  use  the  roller  to  smooth 
or  firm  the  surface  a  light  harrow  should  follow  it  quickly 
in  order  to  prevent  unnecessary  loss  of  soil  moisture,  be- 
cause the  firming  draws  the  deeper  water  to  the  surface, 
the  surface  temperature  becomes  higher  in  the  sunshine 
and  the  wind  velocity  near  the  smooth  surface  is  greater; 
each  of  which  favors  the  rapid  loss  of  water. 

293.  Danger  in  the  Use  of  the  Roller. — On  heavy  soils, 
when  they  are  a  little  wet,  injurious  results  may  follow  the 
use  of  the  roller  just  after  planting  or  seeding  on  account 
of  the  close  packing,  excluding  the  air  from  the  seed,  which 


238  Plvysics  of  the  Soil. 

interferes  with  quick  germination.    This  danger  is  greatest 
where  grain  has  been  sown  with  a  drill. 

The  use  of  the  roller  when  the  soil  is  a  little  too  wet  may 
also  interfere  with  the  formation  of  nitric  acid  in  the  soil 
by  making  it  too  close  and  too  wet.  In  such  a  case  the  im- 
mediate use  of  a  light  harrow  would  only  retain  the  moist- 
ure and  make  the  rate  of  nitrification  slower. 

294.  The  Plow. — The  plow  as  a  tillage  tool  is  usorl  for 
two  distinct  purposes,  1st,  to  alter  the  texture,  forming 


FIG.  76. — Showing  the  principle  of  the  pulverizing  action  of  the  plow. 

from  a  comparatively  hard  soil  a  deep  and  mellow  layer  of 
earth;  2d,  to  bury  beneath  the  surface  weeds  and  other 
vegetation  or  manure  where  it  may  decay  rapidly  and  be 
converted  into  available  plant  food. 

If  you  will  open  a  book,  placing  the  fingers  upon  the  fly 
leaf  in  front  and  the  thumbs  under  the  fly  leaf  in  the  back 
and  abruptly  bend  up  the  corner  it  will  be  seen  that  every 
leaf  is  slipped  over  its  neighbor.  What  takes  place  is  rep- 
resented in  Fig.  76.  Had  pins  been  put  through  the  book 
before  attempting  to  bend  the  leaves  the  bending  would 


Tillage  to  Modify  Soil  Texture.  239 

have  tended  to  cut  the  pins  into  as  many  pieces  as  there 
were  leaves,  just  as  seen  in  Fig.  76. 

Now  the  plow  has  exactly  this  kind  of  effect  upon  the 
furrow  slice;  it  tends  to  make  it  divide  into  thin  layers 
which  slide  over  one  another  just  as  the  leaves  of  the  book 
did,  and  it  is  because  of  this  sort  of  action  that  a  plow  pul- 
verizes a  soil  as  no  other  tool  can. 

295.  How  Plowing  May  Puddle  Soils. — When  a  soil  is  too 
wet  its  granules  are  so  easily  broken  that  the  plow  is  liable 
to  shear  all  the  coarser  ones  into  two,  three,  or  more  slices 
just  as  the  pin  has  been  sliced  in  Fig.  76,  thus  destroying 
its  tilth  by  puddling  it. 

296.  How  Plowing  May  Correct  Texture  and  Improve 
Tilth. — If  a  soil  has  gotten  out  of  tilth,  has  become  cloddy 
or  has  been  partly  puddled  there  is  a  shape  of  mold  board, 
a  stage  of  soil  moisture,  and  a  depth  of  furrow  slice  which 
will  help  to  restore  the  tilth  best  and  quickest.     When  such 
a  soil  is  the  least  amount  too  dry  to  puddle  the  plow  will 
shear  it  into  the  thinnest  slices ;  if  still  drier  the  layers  will 
be  thicker  and  will  form  coarser  granules. 

When  much  too  dry  no  shearing  can  take  place  at  all,  and 
the  furrow  slice  is  simply  broken  into  coarse  lumps. 

If  you  bend  but  a  few  leaves  of  the  book  at  a  time  there 
is  but  little  slipping,  but  the  thicker  the  pile  of  leaves  the 
greater  is  the  sliding  and  the  greater  is  the  tendency  to 
shear.  So  it  is  in  plowing,  the  deep  furrow  pulverizes  bet- 
ter and  puddles  worse  than  the  thin  slice  or  shallow  furrow. 

Again  if  you  bend  the  leaves  gently  there  is  little  shear- 
ing, but  if  abruptly  the  sliding  is  great.  So  if  you  plow 
with  the  low  mold  board  of  Fig.  77  you  disturb  the  tilth 
least,  puddled  the  soil  least,  and  leave  the  texture  coarsest ; 
but  if  the  steep  mold  board  of  Fig.  78  is  used  there  is  the 
greatest  danger  of  puddling  if  the  soil  is  too  wet  and  the 
greatest  opportunity  to  pulverize  the  soil  and  improve  the 
ti  1  th  if  the  moisture  is  right. 

297.  Forms  of  Plows. — Plows  are  made  with  two  funda- 


240  Physics  of  the  Soil. 

mentally  different  shapes  depending  upon  the  character  of 
the  work  which  they  are  expected  to  do. 

If  the  chief  object  of  the  plow  is  to  cut  a  clean  furrow 
slice  and  turn  it  over  so  as  to  completely  cover  whatever 
may  be  upon  the  surface  a  shape  represented  in  Fig.  Y7  is 
used. 


FIG.  77. — Typo  of  sod  plow,  \vhicb  pulverizes  but  little. 

If  on  the  other  hand  the  primary  object  of  the  plow  is  to 
thoroughly  pulverize  the  soil,  making  it  deep  and  mellow, 
a  form  represented  in  Fig.  78  must  be  used.  Then  accord- 
ing as  one  or  the  other  of  these  two  chief  objects  vary  in 
importance  shapes  of  plows  will  be  chosen  which  are  in- 
termediate between  these  two  extremes. 

298.  Kind  and  Condition  of  Soil  and  Shape  of  Plow. — It 
must  be  clear  from  the  mechanical  action  of  the  plow  that 
its  form  should  be  adapted  to  the  soil.  If  the  soil  has  a 
tendency  to  be  too  open  and  porous,  and  is  naturally  coarse 
grained,  like  the  sandy  soils,  it  should  be  plowed  with  a 
steep  mold  board,  a  little  over  wet  and  as  deep  as  other  con- 
ditions will  permit,  so  as  to  break  down  the  granulation 
and  secure  the  closer  texture. 

If  the  soil  is  generally  too  close  in  texture,  is  heavy  and 
soggy,  it  needs  the  less  steep  mold  board  used  when  the  soil 
is  a  little  dry  so  as  to  shear  into  thicker  layers  and  form 
granules  of  larger  size. 

If  plowing  must  be  done  when  the  soil  is  a  little  too  wet 


Forms  of  Plows.  241 

use  the  less  steep  mold  board  and  plow  as  shallow  as  other 
conditions  will  allow. 

If  a  soil  has  become  a  little  too  dry  and  is  not  pulverizing 
fine  enough,  use  the  steeper  mold  board  and  plow  deep  for 
this  will  split  it  into  thinner  layers,  make  the  soil  finer, 
and  the  tilth  better. 

299.  The  Kind  of  Soil,  the  Shape  of  the  Mold  Board,  and 
the  Draft  of  the  Plow. — Since  the  steepest  mold  board  bends 
the  furrow  slice  most  and  pulverizes  most,  it  is  clear  that 
the  work  done  is  greatest,  and  hence  that  the  draft  will  be 
most. 

Since  deep  plowing  pulverizes  more  than  shallow  plow- 
ing the  work  done  is  more  than  in  proportion  to  the  depth. 

Since  clay  soils  have  more  and  larger  granules  which 
must  be  sheared  in  two  in  plowing  than  sandy  soils  do,  the 
labor  of  plowing  must  be  greater. 

Since  the  granules  of  the  soil  are  not  as  strong  when  the 
soil  is  moist  as  when  dry  it  plows  much  easier,  when  in 
good  condition.  But  if  the  soil  has  become  too  dry  and  yet 
must  be  plowed,  it  should  be  plowed  deeper  rather  than 
shallower.  This  is  necessary  to  pulverize  better,  to  get 
more  moist  soil  on  the  surface  for  the  immediate  seed  bed, 
and  to  quicker  moisten  and  bring  into  condition  the  layer 
which  has  become  too  dry. 

300.  The  Sod  Plow — The  sod  or  breaking  plow  is  con- 
structed so  as  to  reduce  the  draft  as  much  as  possible  by 
doing  only  the  work  needed  to  cut  and  turn  over  the  fur- 
row slice.  This  is  accomplished  by  making  the  mold  board 
very  long  and  slanting  so  that  the  furrow  slice  is  bent  and 
twisted  as  little  as  possible,  as  shown  in  Fig.  77 ;  the  chief 
work  being  to  cut  it  and  roll  it  bottom  up. 

The  extremely  oblique  edge  of  the  share  in  the  breaking 
plow  reduces  the  draft  in  cutting  off  the  roots  by  allowing 
the  cutting  to  be  done  gradually  and  with  a  drawing  cut, 
just  as  it  is  easier  to  cut  off  a  limb  by  letting  the  blade  of 
the  knife  slant  backward,  drawing  it  across. 


242 


Physics  of  the  Soil. 


The  extremely  oblique  construction  of  this  plow  too, 
makes  it  easier  to  hold  it  steady  when  passing  and  cutting 
oif  strong  roots  or  other  obstruction. 


FIG.  78. — Type  of  pulverizing  plow  with  steep  moldboard. 

301,  The  Pulverizing  or  Stubble  Plow. — It  will  be  seen 
from  Fig.  78  that  this  plow  has  a  much  steeper  mold  board 
and  much  less  oblique  plowshare,  the  object  being  to  bend 
the  furrow  slice  as  abruptly  as  possible  before  it  is  turned 
over,  for  this  is  what  pulverizes  the  soil,  giving  it  the  loose, 
fine,  open  texture  sought. 

302.  Mellow  Soil  Plows. — Soils  which  are  sandy  and 
naturally  very  mellow  may  be  plowed  with  "a  plow  having 
the  mold  board  less  steep  and  more  like  that  of  Fig.  79  in 
shape.    With  such  a  form  as  this  the  team  may  cut  a  wider 
furrow,  and  thus  cover  the  ground  more  rapidly,  because 
the  draft  is  less. 

When  soils  are  very  heavy  and  stiff  it  may  also  be  de- 
sirable to  use  this  type  of  plow,  simply  because  the  draft 
would  be  too  heavy  for  the  team  with  the  type  which  pul- 
verized the  soil  more. 

Again  very  loose  soils  which  have  an  extremely  fine  tex- 
ture and  tend  to  clog  will  often  clear  better  from  the 
less  steep  mold  board  because  the  pressure  comes  more 
obliquely  against  the  surface. 


Draft  of  Plows. 


243 


303.  Draft  of  Stubble  Plows — The  amount  of  labor  in- 
volved in  plowing  a  field  is  so  large  under  the  best  possible 
conditions,  and  it  is  so  easy  to  make  it  unnecessarily  large, 
that  it  is  important  to  understand  the  principles  upon 
\7hich  the  draft  depends. 

Mr.  Pusey  in  England,  in  1840,  made  a  series  of  trials 
on  the  draft  of  plows  in  soils  of  different  kinds,  using  10 
different  plows.  We  have  combined  his  results  and  give 
them  in  the  table  below: 

Table  showing  the  draft  of  plows  in  tests  made  in  England 
and  in  America. 


Kind  of  soil. 

No.  of 
plows. 

Size  of 
furrow. 

Total 
draft. 

Draft  per  sq. 
in.  of  furrow 

10 

5  in.  x  9  in. 

Lbs. 
227 

Lbs. 
5.04 

10 

5  in.  x  9  in. 

250 

5.55 

10 

5  in.  x  9  in. 

280 

6  22 

10 

5  in.  x  9  in. 

440 

9.72 

Blue  clay  

10 

5  in.  x  9  in. 

661 

14.69 

Sandy  loam  C.T.  C.  Morton)  

5 

6  in.  x  9  in. 

566 

10.48 

Stiff  clay  loam  (N.  Y.  1850)  

14 

1  in.  x  10  in. 

407 

5.bl 

Prof.  J.  "W.  Sanborn  made  an  extended  series  of  trials  in 
1890  in  Missouri  and  later  in  Utah  and  the  average  of  all 
his  trials  gives  a  draft  of  5.98  Ibs.  per  sq.  inch  of  the  cross 
section  of  the  furrow  slice.  Separating  these  trials  historic- 
ally, omitting  those  in  the  blue  clay  in  England,  the  re- 
sults stand: 


English  trials  1840,  mean  draft  7.41  Ibs  per  sq.  Inch. 
American  trials  1850,      "         "    5.81    "     "    "       " 
"  "       1890,     "         "    5.98   "     "    " 


304.  Draft  of  Sod  Plow  With  and  Without  Coulter 'A 

set  of  trials  with  a  sod  plow  near  the  type  of  Fig.  77,  in 
clover  sod  2  years  old, when  the  moisture  present  was  about 
as  high  as  it  is  prudent  to  work  the  soil,  gave  results  as  fol- 
lows: 


244 


Physics  of  the  Soil. 


Size  of  farrow. 

Total   draft. 

Draft  per 
sg.  in. 

Sod  plow  with  wheel  coulter  

5.575  in.x  15.08  in. 
5.325  in.  x  14.5  in. 

Lbs. 
296.25 
313  75 

Lbs. 
3  524 
4.453 

Difference  

47.50 

.929 

Besides  doing  the  work  better  the  coulter  diminished  the 
draft  20.86  percent. 

A  later  series  of  observations  was  made  on  a  clover  sod 
with  the  same  sod  plow  provided  with  a  wheel  coulter,  but 
at  a  time  when  the  soil  was  dryer  than  when  the  other 
measurements  were  made.  The  results  found  were: 


Size  of  furrow. 

Total  draft. 

Draft  por 
sq.  in. 

Clover  sod  without  coulter  .......... 

6.47  x  11.61  in. 

Lbs. 
714  35 

Lbs. 
10  80 

6.413x  12  47  in. 

G61  82 

8  616 

Difference.... 

49.53 

2.184 

In  this  set  of  trials  the  coulter  has  reduced  the  draft 
25.34  per  cent. 

305.  Draft  of  Sod  Compared  With  Stubble  Plow. — Another 
set  of  trials  were  made  at  the  time  of  (304)  to  compare  the 
stubble  type  of  plow,  Fig.  78,  with  that  of  Fig.  77,  and  the 
results  are  given  below: 


Size  of  furrow. 

Total   draft. 

Draft  per 
sq.  inch. 

5.872  x  14.31  in. 

Lbs. 
452  4 

Lbs. 

5  384 

Sod  plow  without  coulter  

5.325  x  14.5  in. 

313.75 

4.453 

Difference  

108.65 

.931 

In  this  case  the  shape  of  the  plow  altered  the  draft  20.9 
per  cent.,  and  the  difference  is  probably  a  measure  of  the 
difference  in  the  amount  of  pulverizing  done  by  the  two 
plows. 


Draft  of  Plows. 


245 


306.  Influence  of  Difference  of  Soil  Moisture  on  the  Draft 
of  Plows — By  combining  the  data  in  the  two  tables  of  (304) 
with  reference  to  the  degree  of  moisture  in  the  soil  when 
the  trials  were  made  we  have  the  results  given  below. 


Sod  plow  with  coulter. 
Draft  per  sq.  in. 

Sod  plow  without  coulter. 
Draft  per  sq.  in. 

Soil  rather  dry  

8.616 

10.80 

Soil  in  best  condition.  .. 

3.524 

4.453 

5.092 

6.347 

From  this  comparison  it  is  clear  that  the  draft  of  the 
plow  is  very  much  modified  by  the  condition  of  the  soil. 
The  results  show  the  draft  more  than  doubled  when  the 
soil  was  dryer. 


FIG.   79.— Type  of  moldboard  suited   to  mellow  soils  requiring  little  pul 

verizing. 

307.  The  Draft  of  Sulky  Plows — It  is  generally  claimed 
that  the  draft  of  sulky  plows  is  less  than  that  of  the  free- 
swimming  types  because  the  friction  of  the  sole  and  land- 
side  is  transferred  to  the  well  oiled  bearings  of  the  carriage. 
The  few  records  accessible  do  not  show  a  material  gain, 
when  the  influence  of  the  weight  of  the  carriage  and  driver 
are  not  deducted,  but  where  the  draft  is  no  greater  on  the 
team  with  the  man  riding  than  when  walking,  and  the  plow 
16 


246 


Physics  of  the  Soil. 


can  be  handled  with  equal  facility,  there  is  an  evident  ad- 
vantage in  riding  plows  such  as  Fig.  80. 


FIG.  80. — Sulky  or  riding  plow. 


308.  The  Line  of  Draft.— It  is  very  important  in  the 
handling  of  a  plow  that  the  line  of  draft  be  just  right  and 
such  that  a  line  connecting  the  center. of  draft  A,  Fig.  81, 
in  the  mold  board  with  the  place  of  attachment  to  the  plow 
bridle  shall  also  lie  in  the  plane  of  the  traces,  as  shown  in 


PIG.  81.— Direction  of  the  Mne  of  draft  for  plows. 


Care  of  Plows.  247 

the  cut.  by  the  line  A,  B,  D.  If  for  any  reason  the  line  of 
draft  becomes  a  broken  one  as  A,  C,  D  or  1,  3,  5  or  1,  4,  5 
instead  of  1,  2,  5  the  draft  of  the  plow  is  made  heavier. 

The  greatest  care  should  be  exercised  to  have  the  length 
of  the  traces,  or  the  hitch  at  the  plow  bridle  such  that  the 
plow  "swims  free,"  requiring  little  or  no  pressure  at  the 
handles  to  guide  it.  If  a  steady  pressure  in  any  direction 
is  required  at  the  handles  something  is  wrong  and  the  team 
is  doing  more  work  than  is  necessary  as  well  as  the  man 
holding  the  plow. 

309.  The  Securing  of  Plows. — There   are   certain   soils, 
whose  texture  is  such  that  the  most  perfect  plow  surface 
fails  to  shed  them  completely  and  in  such  cases  tlie  shapes 
approaching  the  sod-plow  are  more  successful.     But  it  is 
a  matter  of  greatest  moment  that  the  mold  board  possess 
not  only  an  extremely  hard  finish,  so  as  not  to  be  scratched 
by  stone  or  grit  in  the  soil,  but  it  must  also  possess  an  ex- 
tremely close  texture  so  as  to  be  susceptible  of  a  very  high 
polish.     If  the  metal  itself  is  coarse  grained  there  will  be 
inequalities  even  in  the  bright  surface  in  which  the  fine  soil 
particles  may  lodge  and  thus  clog  the  plow. 

310.  Care  of  the  Plow. — Too  great  pains  cannot  be  taken 
to  maintain  a  bright  clean  surface  on  all  polished  parts  of 
the  plow  and  the  necessary  care  to  do  this  will  always  pay; 
this  caution  is  doubly  important  where  the  soils  are  in- 
clined to  clog. 

Whenever  a  plow  is  laid  by,  even  for  a  few  weeks,  its 
bright  surfaces  should  be  thoroughly  cleaned,  wiped  dry 
and  coated  with  a  layer  of  the  thick  mineral  lubricant  used 
for  journal  bearings,  to  prevent  rusting.  A  little  rusting 
may  practically  ruin  a  plow  for  use  in  a  soil  which  tends  to 
clog  and  a  single  winter  of  rusting  may  injure  a  plow  more 
than  a  full  season  of  heavy  service  in  the  field. 

311.  Keeping  the  Plow  in  Form. — A  plow  cannot  render 
heavy  and  long  continued  service  without  getting  out  of 
proper  form.       The  point  becomes  dull,  too  short  and  as- 


248 


Physics  of,  the  Soil. 


sumes  the  form  shown  in  Fig.  82,  instead  of  that  in  Fig. 
83.     In  this  worn  condition  the  inclination  of  the  mold 


FIG.  82. — Showing  point  of  plow  worn  into  bad  form. 

board  to  the  furrow  slice  is  changed,  the  plow  tends  to  run 
on  its  point,  is  more  difficult  to  hold,  the  draft  becomes 
heavier  and  poorer  work  is  done  with  it. 


FIG.  83.— Showing  point  of  plow  in  good  form. 

The  heel  of  the  share  C  in  Figs.  84  and  85  is  especially 
liable  to  get  into  bad  form  and  dull,  causing  the  plow  to 


FIG.  84.— Showing  heel  of  plow  in  form  for  dry  soil. 

wing  over  to  the  land  and  draw  harder,  not  only  because  it 
is  dull  but  because  a  steady  pressure  must  be  exerted  at  the 
handles  to  prevent  the  plow  from  tipping  to  land. 


FIG.  85. — Showing  heel  of  plow  in  form  for  moist  soil. 

It  is  sometimes  necessary  to  change  the  form  of  the  plow 
to  suit  a  harder  or  more  mellow  condition  of  the  soil.  When 


Jointer  Attachment  of  Plows. 


249 


the  soil  is  dry  and  hard  the  heel  needs  to  be  set  down,  as 
shown  at  C,  Fig.  84,  and  the  point  may  need  to  dip  even 
more  than  in  Fig.  83,  but  when  the  soil  is  wet  and  mellow 
the  shape  shown  in  Fig.  85  is  required  to  prevent  it  draw- 
ing too  deeply  into  the  ground. 

In  taking  the  share  to  the  shop  for  sharpening  or  setting 
the  landside  should  accompany  it  in  order  that  the  black- 
smith may  have  a  guide  in  giving  it  the  proper  shape. 

312.  The  Jointer  Attachment. — One  of  the  most  useful 
attachments  for  a  plow  is  known  as  a  jointer,  represented 
in  Fig.  86.  This  tool  is  used  to  great  advantage  when  con- 
siderable material  needs  to  be  turned  under,  such  as  long 
stubble,  coarse  manure  or  in  turning  under  a  green  crop 
for  manure.  When  this  is  used  with  the  drag  chain  in  the 
furrow  very  long  weeds  can  be  completely  laid  under  the 
surface,  leaving  the  ground  in  excellent  shape. 


FIG.  86.— Plow  with  jointer. 

When  sod  ground  is  to  be  plowed  deep  and  left  in  shape 
for  immediate  pulverizing  to  fit  it  for  crops  this  tool  will 
often  render  excellent  service  by  cutting  out  a  section  of 
the  sod,  turning  it  into  the  bottom  of  the  furrow,  where  it 
will  be  completely  covered,  at  the  same  time  leaving  the 
upper  edge  of  the  furrow  slice  composed  only  of  compara- 
tively loose  earth. 


250 


Physics  of  the  Soil. 


313.  Subsoil  Plow. — One  of  the  most  widely  used  forms 
of  sub-soil  plow  is  represented  in  Fig.  87.  It  is  intended 
to  be  used  in  the  bottom  of  an  ordinary  furrow,  one  plow 
following  the  other  in  doing  the  work. 

Extremely  good  judgment  is  required  in  the  use  of  the 
subsoil  plow  to  avoid  puddling,  which  is  sure  to  result  from 
using  the  tool  when  the  subsoil  is  too  wet.  In  humid 
climates  the  dangers  are  greatest  in  the  spring  and  least 
in  the  fall,  and  it  must  be  kept  in  mind  that  the  surface 
soil  may  be  in  good  condition  to  plow  when  the  subsoil  is 
much  too  wet. 


FIG.  87.— Sub-soil  plow. 

In  semi-arid  climates  the  dangers  of  injuring  the  soil 
texture  are  much  less  and  it  is  under  such  conditions  that 
subsoiling  is  likely  to  prove  most  profitable,  tending  as  it 
does  to  increase  the  available  moisture  for  crop  production. 


OBJECTS,   METHODS  AND  TIMES  OF   PLOWING. 

314.  Depth  of  Plowing. — The  best  depth  to  plow  at  a 
given  time,  on  a  given  soil,  for  a  given  crop  must  be  de- 
cided on  the  spot  after  exercising  good  judgment  with  a 


Best  Conditions  o/  Soil  for  Plowing.  251 

knowledge  of  the  needs  and  conditions.  There  can  be  no 
"rule  of  thumb"  for  plowing. 

As  a  general  rule  in  humid  climates  the  plow  never 
should  go  deeper  than  to  turn  over  the  surface  or  dark 
colored  layer  of  weathered  soil.  If  deeper  plowing  is  done, 
turning  up  the  unweathered  subsoil,  the  productiveness 
of  the  field  will  be  reduced. 

It  is  very  desirable  to  develop  and  maintain  a  deep  soil; 
this  is  clearly  proved  by  the  heavier  crops  which  always 
grow  upon  "back  furrows"  and  the  scanty  ones  which  grow 
in  "dead  furrows"  as  compared  with  the  rest  of  the  field. 
When  a  soil  is  thin  and  the  subsoil  is  close  and  heavy  it  is 
only  safe  to  deepen  it  gradually  by  plowing  a  little  deeper 
each  year  or  two,  turning  under  as  far  as  possible  coarse 
manure,  stubble  and  green  crops  to  make  the  soil  open  and 
form  humus  in  it. 

Fall  plowing  may  usually  be  as  deep  as  the  soil  will  per- 
mit, down  to  6,  7  or  even  8  inches,  but  the  cases  are  rela- 
tively few  where  it  is  important  to  plow  deeper  than  6  or  7 
inches.  Where  plowing  is  for  small  grains  to  be  sowed  at 
onoe  the  depth  may  usually  be  shallow,  5  inches  or  less,  as 
these  thrive  best  in  a  shallow  seedbed. 

315.  Best  Condition  of  Soil  for  Plowing. — There  is  a  con- 
dition of  moisture  peculiar  to  each  and  every  soil  at  which 
it  will  be  left  with  the  best  texture  after  plowing,  requiring 
the  least  amount  of  finishing  work  to  put  it  in  final  condi- 
tion. If  the  soil  is  too  wet  the  crumb  structure  so  essen- 
tial to  a  clay  soil  will  be  partly  destroyed  and  the  soil 
puddled;  if  too  dry  the  furrow  slice  will  not  shear  in  thin 
layers  and  the  soil  will  not  be  pulverized  fine.  The  water 
content  should  be  such  that  the  damp  soil  squeezed  in  the 
hand  will  hold  its  form  but  will  easily  crumble  to  pieces 
and  not  be  at  all  pasty. 

Sod  ground  can  always  be  plowed  a  little  wetter  than 
corn,  potato  or  stubble  ground  because  the  roots  lessen  the 
danger  of  puddling  and  the  shearing  effect  of  the  plow  is 
less. 


252  Physics  of  the  Soil. 

316.  Treatment    of    Ground    After    Plowing. — Ground 
plowed  late  in  the  fall,  to  act  as  a  mulch,  to  allow  the 
moisture  to  penetiate  deeply  and  to  have  its  texture  altered 
by  thawing  and  freezing,  should  be  left  with  the  natural 
furrow  surface  rough  and  uneven. 

If  plowed  in  the  spring  when  the  ground  is  a  little  over 
wet  and  the  turned  furrow  shows  large  polished  surfaces 
the  ground  should  be  gone  over  with  a  harrow  but  not  im- 
mediately, for  if  the  soil  is  a  little  too  wet  it  should  be  al- 
lowed to  dry  just  enough  so  as  to  crumble  perfectly. 

If  the  soil  is  already  a  little  too  dry  and  a  crop  is  to  be 
put  on  at  once  then  the  harrow  should  follow  the  plow 
olosely,  otherwise  the  soil  will  become  lumpy  and  the 
whole  furrow  slice  may  become  too  dry  for  the  best  germi- 
nation. 

If  the  plowing  is  for  corn,  potatoes  or  the  garden  and  is 
done  some  time  before  the  ground  is  to  be  planted  then  the 
surface  is  better  left  as  it  would  be  for  fall  plowing,  pro- 
vided the  soil  is  in  good  condition  when  plowed,  because 
it  will  form  a  better  mulch,  it  will  take  the  rains  better, 
be  less  likely  to  become  too  much  compacted  by  the  rains 
and  will  harrow  down  better  when  planting  time  comes. 

317.  Plowing  for  Corn  in  the  Fall — On  soils  which  are 
naturally  mellow,  where  large  areas  are  to  be  planted  and 
the  spring's  work  is  crowded  it  is  often  best  to  plow  for 
corn  late  in  the  fall,  just  before  freezing.    If  such  ground 
is  to  be  manured  it  can  be  plowed  in  then  to  advantage  or 
if  the  manure  is  not  too  coarse  it  may  be  applied  as  a  sur- 
face dressing  during  the  winter  and  disked  in  the  spring. 
If  the  soils  are  very  heavy  and  have  a  tendency  to  run  to- 
gether with  the  spring  rains  then  there  is  danger  that  the 
disc  may  not  be  able  to  bring  the  field  into  condition. 

318.  Plowing  Sod. — There  are  two  methods  of  plowing 
sod,  1st,  skim-plowing,  usually  in  the  fall,  turning  over  a 
thin  sod  to  kill  the  turf,  expecting  to  cross  plow  in  the 
spring  deep  enough  to  bury  the  sod  and  turn  up  enough 


Plowing  Under  Manure.  253 

soil  to  work  up  fine  and  form  the  seed  bed.  2d.  Plowing 
deep  enough  at  first  to  provide  a  sufficient  soil  to  work  up 
with  a  disc  harrow  and  give  the  desired  depth  of  seed-bed. 
The  latter  method  usually  requires  less  time  but  the  draft 
is  heavier.  It  is  usually  best  in  such  cases  to  go  over  the 
surface  with  a  heavy  roller  to  press  the  sod  home  and  lessen 
the  danger  of  the  disc  turning  them  over. 

319.  Plowing  Under  Manure. — If  manure  is  coarse  or  the 
soil  light  it  is  usually  better  to  place  it  under  a  deep  furrow 
because  it  needs  more  moisture  to  rot  it  and  in  heavy  soils 
it  will  let  the  air  penetrate  more  deeply  into  the  soil.       In 
such  cases  it  is  better  to  do  the  plowing  in  the  fall  or  as 
early  in  the  spring  as  the  soil  will  permit.     If  the  ground 
is  a  little  too  dry  when  plowed  and  seeding  time  is  at  hand 
the  field  should  be  thoroughly  harrowed  and  firmed,  using 
the  heavy  roller  if  necessary  in  order  to  'establish  good 
capillary  connection  with  the  deeper  soil.     If  this  is  not 
done  the  soil  above  is  liable  to  become  too  dry. 

When  the  manure  is  well  rotted  it  may  be  left  nearer  the 
surface  to  advantage,  except  in  the  sandy  soils  where  the 
air  penetrates  so  deeply  as  to  cause  too  rapid  decomposition 
of  the  manure. 

320.  Plowing  Under  Green  Manure — Where  a  crop  is 
turned  under  for  green  manure  it  is  usually  best  to  plow 
deep,  to  use  the  jointer  and  the  drag-chain  if  necessary  to 
get  everything  well  and  deeply  buried.     If  a  considerable 
body  of  material  is  turned  under  thorough  firming  of  the 
soil  after  plowing  will  be  beneficial. 

In  green  manuring  good  judgment  is  always  required 
not  to  let  the  crop  turned  under  exhaust  the  soil  moisture 
too  completely,  for  when  this  has  occurred  a  new  crop 
starts  under  very  unfavorable  conditions,  both  because  of 
lack  of -water  and  immediately  available  plant  food,  for  the 
soluble  salts  are  used  up  with  the  water  by  the  green  ma- 
nure crop. 


2  54:  Physics  of  the  Soil. 

320.  Early  Fall  Plowing — In  regions  and  at  times  where 
there  is  a  deficiency  of  rain,  where  the  soil  is  light  and 
when  the  amount  of  soil  leaching  is  small  it  is  often  de- 
sirable to  plow  as  early  in  the  fall  as  the  crop  has  been  re- 
moved from  the  ground,  in  order  to  save  soil  moisture  and 
to  enable  the  nitrates  and  other  soluble  salts  to  develop  in 
sufficient  quantity  for  the  next  season.  Where  crops  hold 
the  soil  moisture  low  it  may  even  become  necessary  in 
dry  climates  to  raise  one  only  every  other  year  because 
the  plant  food  and  the  crop  cannot  be  produced  by  the 
available  moisture  of  a  single  season.  But  early  fallowing 
in  the  fall  will  often  render  the  full  year  unnecessary. 


GROUND  WATER,  WELLS  AND  FARM 
DRAINAGE. 


CHAPTEK  XII. 
MOVEMENTS  OF  GROUND  WATER. 

Of  the  water  which  falls  upon  the  land  one  portion  finds 
its  way  at  once,  by  surface  flow,  into  drainage  channels;  a 
second  portion  is  evaporated  where  it  fell,  while  a  third 
enters  the  ground.  That  portion  which  enters  the  ground 
and  is  not  returned  by  capillarity  or  root  action  constitutes 
the  body  of  ground  water  which  is  the  source  of  supply  for 
wells  and  springs  and  which  requires  removal  by  land 
drainage  when  too  close  to  the  surface. 

322.  Amount  of  Water  Stored  in  the  Ground. — In  most 
localities  after  passing  a  certain  distance  below  the  earth's 
surface  a  horizon  is  reached  where  the  pore  space  in  the 
soil,  sand  and  rock  is  filled  with  water  or  nearly  so.  When 
these  pore  spaces  are  large,  so  that  water  can  flow  through 
them  readily,  wells  sunk  beneath  the  surface  fill  with  water 
to  the  level  of  the  ground  water  surface. 

In  sands  and  sandstones  lying  below  drainage  outlets 
the  amount  of  water  may  be  as  high  as  15  to  38  per  cent, 
of  the  total  volume  of  the  rock  so  that  where  a  country  is 
underlaid  with  broad  and  thick  sheets  of  sandstone,  such 
as  the  Potsdam  and  St.  Peters  in  Wisconsin  and  further 
south,  or  the  Dakota  formation  in  the  west,  there  is  the 
equivalent  of  from  15  to  38  feet  of  water  on  the  level  for 
every  100  feet  in  thickness  of  the  rock  formation,  and 


256       Ground  Water,  Wells  and  Farm  Drainage. 

abundant  supplies  of  water  can  always  be  found  in  such 
places. 

The  loose  sands  and  gravels  have  a  pore  space  of  20  to 


Fio.    88.— Contour   map  of  a   field,   one   portion   of   which   has   been    tile 

drained. 

38  per  cent,  of  their  volume  so  that  where  these  lie  below 
the  ground  water  surface  and  their  volume  is  large  an 
abundance  of  water  exists. 


Ground  Waier  Surface. 


257 


In  the  soils  and  clays  the  pore  space  is  even  larger  than 
it  is  in  the  sands  and  this  too  may  be  filled  with  water  but 
here  the  texture  is  usually  so  close  that  a  well  sunk  in  such 


FIG   89.— Contour   map   of   the   ground    water   surface    under   the    field    of 

Fig.  88. 

material  fills  with  water  so  slowly  that  they  cannot  serve 
as  sources  of  water  supply. 

Even  in    the    hard    crystalline  rock,  like  marble  anc( 


258       Ground  Water,  Wells  and  Farm  Drainage. 

granite,  there  may  be  as  much  as  A  of  a  pound  of  water 
in  each  cubic  foot,  but  here  again  the  texture  is  too  close  to 
permit  such  water  to  become  available  in  wells. 

323.  The  Ground  Water  Surface. — As  the  rains  which  fall 
in  a  given  locality  percolate  beneath  the  surface  they  fill 
the  pore  spaces  between  the  soil  grains  and  raise  the  level 
of  the  ground  water.  If  none  of  this  water  drained  away 
and  none  of  it  were  lost  by  evaporation  the  whole  soil 
would  have  its  pore  spaces  filled  with  water  and  the  surface 
of  the  ground  water  would  coincide  with  the  surface  of  the 
land.  As  it  is,  as  soon  as  the  surface  of  the  ground  water 
ceases  to  be  level  drainage  begins  and  the  water  under  the 
higher  land  is  lowered  until  a  condition  is  reached  when 
the  rate  of  drainage  laterally  exactly  equals  the  rate  of  ac- 
cumulation of  water  from  the  rains. 

In  Figs.  88  and  89  are  shown  the  contours  of  the  surface 
of  a  section  of  land  and  of  the  ground  water  beneath,  both 
sets  of  contours  being  referred  to  the  same  datum  plane, 
Lake  Mendota,  into  which  the  water  is  draining.  Here,  it 
will  be  seen,  the  ground  water  stands  highest  where  the 
surface  is  highest  and  lowest  where  the  land  is  lowest.  The 
arrows  show  the  lines  of  flow  and  make  it  clear  why  the  tile 
drained  area  needed  that  treatment. 


FIG.   90.— Showing  lines  of  flow  of  ground  water  during  seepage  into  a 

stream. 

324.  Seepage — Almost  everywhere  under  the  land  areas 
there  is  a  slow  movement  of  the  ground  water  from  higher 
to  lower  levels  destined  ultimately  to  reach  some  drainage 
outlet.  This  movement  is  known  as  seepage  and  Fig.  90  13 


Ground  Water  Surface. 


259 


a  cross-section  showing  how  the  water  flows  from  the  ad- 
jacent higher  lands  and  enters  the  channels  of  streams,  the 
beds  of  lakes  and  even  the  ocean  itself. 


l«'iu    91.— Showing  contours'  of  ground  water  surface  in  the  vicinity  of 
Los  Angeles  River,  Cal. 

325.  Growth  of  Streams — The  water  which  maintains 
the  low  stage  flow  of  streams  finds  its  way  into  channels 

all  along  the  banks  and  bot- 
toms rather  than  at  isolated 
places  in  the  form  of  springs, 
entering  in  the  manner 
stated  in  (324).  In  Fig.  91 
is  represented  the  ground 
•ater  surface  in  the  valley  of 
the  Los  Angeles  river,  Cali- 
fornia, where  it  is  seen  to 
rise  back  from  the  stream 
and  up  the  valley.  This 
river  must  be  draining  the 

seepage  in  25,978  feet.  adjacent  higher   land  and  it 

was  found  by  actual  measurement  that  the  growth  of  this 
stream  in  11  miles  was  60  cubic  feet  of  water  per  second; 
the  water  all  entering  by  slow  general  seepage,  there  being 


r 


260       Ground  Water,  Wells,  and  Farm  Drainage 

no  visible  springs  or  streams  anywhere  along  the  line. 
Fig.  92  shows  the  increase  in  25,978  feet,  determined  by 
gauging. 

326.  Changes  in  the  Level  of  the  Ground  Water. — The 
level  of  the  ground  water  in  a  given  section  is  usually  sub- 
ject to  changes,  the  surface  rising  and  falling  with  the  sea- 
son and  with  the  rainfall  of  the  place.  The  change  may  be 
as  much  as  5  or  6  feet  in  a  single  season,  as  represented  in 
Fig.  93,  and  when  a  series  of  dry  or  of  wet  years  follow  in 


\VMLl2 

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9          J 

I           J 

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J           J 

4.          3 

r.       J 

f          J 

r        Jf 

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JuritSJL- 



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i  June 

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- 

FIG   93.— Sliowiug  changes  in  the  level  of  the  ground  water  surface  during 

the  season. 

succession  the  changes  may  be  larger  than  this.  It  is  clear 
from  these  facts  that  in  digging  wells  whose  water  comes 
from  near  the  surface  of  the  ground  water  the  bottom 
should  be  carried  deep  enough  into  the  water  bearing  beds 
to  leave  it  below  the  lowest  stages  of  the  ground  water. 

327.  Elevation  of  the  Ground  Water  through  Precipitation 
and  Percolation. — In  Fig.  94  is  represented  the  unoccupied 
space  in  eight  feet  of  five  grades  of  sand,  above  standing 
water,  after  2.5  years  had  been  allowed  for  percolation 
under  conditions  where  no  evaporation  could  take  place 
from  the  surface.  The  unshaded  portions  of  this  figure 
represent  the  relative  amounts  of  space  into  which  rains 
may  percolate  for  each  grade  of  sand,  as  compared  with 
the  whole  area  of  the  diagram;  that  is  to  say,  if  an  inch  of 
rain  were  to  fall  upon  the  whole  surface  of  the  diagram 
and  it  were  occupied  with  the  ISTo.  1-00  sand  the  space 
into  which  the  rain  could  descend  is  measured  by  the  un- 
shaded area  under  100;  so  for  each  of  the  other  sands, 


Ground  Water  Surface. 


261 


It  will  be  seen  from  the  diagram  that  up  to  12  inches 
above  the  ground  water  surface  the  space  into  which  water 
can  settle  in  either  sand  is  very  small  and  hence  that  a 
small  amount  of  percolation  will  produce  a  relatively  large 
elevation  of  the  ground  water  surface  at  first. 


FIG.  S3. — Showing  the  aniouut  of  unoccupied  snace  in  completely  drained 
sands.    Space  between  long  rules,  one  foot. 

In  a  tank  filled  with  rather  coarse  sand  and  provided  with 
glass  gauge  tubes,  as  represented  in  Fig.  112,  p.  293,  to 
show  the  level  of  the  ground  water  surface,  a  single  pound 
of  water  added  to  the  14  square  feet  of  surface  raised  the 
level  of  the  ground  water  .31  inch.  In  another  trial 
16.435  Ibs.  of  water  or  .226  inch  raised  the  surface  6.7 
inches.  In  still  another  trial  the  withdrawal  of  33.575  Ibs. 
of  water  from  the  tank,  or  .461  inch,  lowered  the  ground 
water  9.05  inches. 

In  the  table  below  are  given  the  amounts  of  water  re- 

Tdble  showing  amount  of  rain  necessary  to  raise   level  of 
ground  water  after  thorough  drainage. 


Grade  of  sand. 

Ifoot. 

2  feet. 

3  feet. 

4  feet. 

No.  20  

Inche». 
0.874 

Inches. 
4.379 

Inches. 
8  550 

Inches. 
12.81 

No.  40  

.4:i3 

3.551 

7.795 

12  19 

No.  60  

.579 

2.701 

6.454 

10  80 

No  80.               

.370 

1.592 

4  080 

7.573 

No.  100  

.242 

1.030 

2.635 

5.131 

17 


262       Ground  Water,  Wells,  and  Farm  Drainage 

quired  to  raise  the  surface  of  the  ground  water  1,  2,  3  and 
i  feet  in  the  sands  of  Fig.  94,  after  thorough  drainage  has 
taken  place. 

328.  Law  of  Flow  of  Water  Through  Sands  and  Soils. — It 
has  been  generally  claimed  that  the  velocity  of  flow  of 
water  through  sands  and  soils  is  directly  proportional  to 
the  effective  pressure  and  inversely  proportional  to  the 
length  of  the  column  through  which  the  flow  is  taking 
place.  This  means  that  to  double  the  pressure  will  double 
the  rate  of  flow  but  to  double  the  length  through  which 
the  water  must  flow  will  decrease  the  rate  one  half.  A 
law  analogous  is  formulated  for  the  flow  of  fluids  through 
capillary  tubes  and  under  certain  conditions  of  pressure 
and  dimensions  the  law  has  been  nearly  fulfilled,  both  with 
sands  and  capillary  tubes. 

In  practical  measurements1  of  flow  it  is  found  that  the 
flow  through  some  sands  and  some  capillary  tubes  increases 
faster  than  the  pressure  while  in  others  it  does  not  increase 
so  rapidly. 

The  law  of  flow  here  referred  to  has  been  designated 
"Darcy's  Law"  and  has  been  expressed  by  the  formula 


where 

V  is  the  velocity, 

P  is  the  difference  in  pressure  at  the  ends  of  the  column, 
h  is  the  length  of  the  column. 

k  is  a  constant  depending  upon   the  size  of  the  soil  grains,  the 
amount  of  pore  space  and  the  viscosity  of  the  fluid. 

329.  To  Compute  Flow  of  Water  Through  a  Column  of 
Sand,  Soil  or  Rock. — Under  the  conditions  where  Darcy's 
law  may  be  fulfilled  the  amount  of  discharge  may  be  com- 
puted by  means  of  the  formula  derived  by  Slichter2  and 
given  below: 

1  Nineteenth  Annual  Report,  U.  S.  Geol.  Survey,  Part  II.,  p.  202. 
'Nineteenth  Annual  Report,  U.  S.  Geol.  Survey,  Part  II.,  pp.  301-322. 


Flow  of  Ground  Water.  263 

T)cl^  S 

q  =  10.22  c.  c.  per  second  (1) 

where 

p  is  the  pressure  in  c.  m.  of  water  at  4°  C. 
d  is  the  diameter  of  the  soil  grains  in  millimeters. 
s  is  the  area  of  the  cross-section  in  sq.  c.  m. 
//  is  the  coefficient  of  viscosity. 
h  is  the  length  of  the  column. 

k  is  a  constant  whose  log.  is  taken  from  the  table,  p.  123. 
and  10.22  is  a  constant  whose  log.  is  [1.0094.] 

If  the  pressure  is  measured  in  feet  of  water  at  4°  C.,  the 
length  in  feet,  the  area  of  cross  section  in  square  feet,  the 
time  in  minutes  and  the  diameter  of  the  soil  grains  in  mil- 
limeters the  formula  is 

T)(12  g 

q  =  .2012      ,   .    cubic  feet  per  minute.  (2) 

juh  k 

If  the  flow  of  water  occurs  under  a  temperature  of  10° 
C.  or  50°  F.  the  formula  may  be  written 

q  =  15.30      ,    .     cubic  feet  per  minute.  (3) 

Jl   K. 

Problem.  —  A  cylinder  4  feet  long,  having  a  cross  sec- 
tion of  2  sq.  ft.,  is  filled  with  sand  whose  grains  have  an 
effective  diameter  of  .15  mm.  What  will  be  the  flow  of 
water  through  it  under  an  effective  pressure  of  12  feet, 
when  the  temperature  is  50°  F.  and  the  pore  space  is  35 
per  cent.  ? 

Substituting  these  values  in  equation  (3)  we  get,  taking 
the  value  of  k  from  the  table,  page  123. 


15.3     4X3162      =  -06532  cu.  ft.  per  minute. 

Problem.  —  What  would  be  the  flow  in  cubic  feet  per 
iminute  under  the  same  conditions  except  at  a  temperature 
df  68°  instead  of  50°  F.  ?  In  this  case  use  formula  (2) 
and  the  results  are,  taking  the  coefficient  of  viscosity  at 
08°  F.  at  .0101  from  the  table  below: 


264:      Ground  Water,  Wells,  and  Farm  Drainage. 


ft- 


TABLE  III. —  Coefficients  of  viscosity  for  tvater  for  various  tem- 
peratures centigrade. 


0=tempera- 
ture 

/^coefficient 
of 

0=tempera- 
ture 

//^coefficient 
of 

centigrade. 

viscosity. 

centigrade. 

viscosity. 

0 

0.0178 

10 

0.0131 

1 

0.0172 

11 

0.0128 

2 

0.0166 

12 

0.0124 

3 

0.0161 

13 

0.0120 

4 

0.0156 

14 

C.0117 

5 

0.0152 

15 

0.0114 

6 

0.0147 

16 

0.0111 

7 

0.0143 

17 

0.0109 

8 

0.0138 

18 

0.0106 

9 

0.0135 

19 

0.0103 

10 

0.0131 

20 

0.0101 

330.  Observed  and  Computed  Flows  Compared — When 
sands  have  bee.n  sorted  into  grades  of  nearly  uniform  size 
and  the  effective  diameter  determined  by  the  method  of 
(143)  and  then  the  flow  of  water  through  them  measured 
in  such  an  apparatus  as  is  represented  in  Fig.  95  the  ob- 
served and  computed  flows  are  related  as  given  in  the  next 
table. 


FIG.  95. — Showing  apparatus  for  measuring  the  flow  of  water  through 
sands  and  the  relations  of  flow  to  the  diameters  of  the  sand  grains. 
Lines  show  theoretical  flow;  dots,  observed  flow. 


Flow  of  Ground  Water. 


265 


-1- '"^T     -^    f  ._,. 


FIG.  96.— Showing  the  sand  grains  referred  to  In  table  on  p.  266.    Natural 

size. 


266       Ground  Water,  Wells  and  Farm  Drainage. 


Table  showing  observed  and  computed  flow  of  water  through 
simple  sands  of  different  diameters  under  a  pressure  of 
I  c.  m.  of  water. 


Grade  of 
sand. 

Diameter  of 
grains. 

Observed 
flow. 

Computed 
flow. 

m.  m. 

gms. 

gms. 

8 

2.54 

2,296 

2,277 

7 

1.808 

1,080 

1,132 

6 

1.451 

756 

757 

Mi 

1.217 

542 

522 

5 

1.095 

504.6 

453.2 

4 

.9149 

329.2 

297.5 

3 

.7988 

210.0 

193 

2 

.7146 

138.6 

122 

1 

.6006 

94.8 

80.6 

0 

.5169 

72.3 

66.8 

The  agreement  between  the  observed  and  computed  flows 
is  not  as  close  as  could  be  wished  but  when  it  is  observed 
that  the  flow  of  air,  from  which  the  diameters  were  com- 
puted, was  not  measured  through  the  same  sample  as  the 
one  through  which  the  flow  of  water  was  measured,  that 
the  pieces  of  apparatus  were  not  the  same  and  that  the  flow 
varies,  theoretically,  as  the  squares  of  the  diameters  of  the 
soil  grains,  it  must  be  conceded  that  there  is  much  more 
than  a  chance  agreement. 

The  samples  of  sand  used  in  these  trials  are  represented 
full  size  in  Fig.  96. 

331.  Relation   of   Observed   Flow   to   Diameter   of   Soil 
Grains. — If  the  squares  of  the  diameters  of  the  sand  grains 
represented  in  Fig.  96  are  plotted  as  abscissas  and  the  ob- 
served and  computed  flows  as  ordinates  their  relations  will 
be  as  shown  in  Fig.  95,  where  it  is  clear  that  the  rates  are 
such  as  to  agree  reasonably  well  with  the  squares  of  the 
diameters  of  the  grains. 

332.  Relation  of  Pressure  to  Flow  Through  Sands. — Most 
experimenters  along  this  line  have  found  that  while  there 
is  a  general  tendency  for  the  flow  to  increase  directly  as  the 
pressure  there  are  nevertheless  conditions  which  prevent 


Flow  of  Ground  Water. 


267 


these  relations  being  realized  in  experiment,  in  some  cases 

the  flow  being  systematically  too  fast  and  in  others  too  slow. 

A  series  of  observations  by  Welitsdhkowsky  and  Wollny 


FIG.  97.— Showing  apparatus  of  Welitschkowsky  and  the  relation  of  pres- 
sure to  flow  of  water  observed  by  him. 

and  the  apparatus  with  which  they  were  secured  are  repre- 
sented in  Fig.  97.  It  will  be  observed  that  where  the  col- 
umns of  sand  used  by  Welitschkowsky  were  25  c.  m.  and 


2 08       Ground  Water,  Wells,  and  Farm  Drainage. 

50  c.  m.  long  the  flow  increased  faster  than  the  pressure ; 
but  when  the  column  was  75  c.  m.  long  the  flow  increased 
directly  as  the  pressure,  while  when  it  was  made  100  c.  m. 
long  then  the  flow  did  not  increase  as  rapidly  as  the  pres- 
sure. 


zoo  cm         100  eoo  aoo          o     tooocm 


FIG.   98. — Showing   the   observed   relation    of   pressure   to    flow   of   water 
through  sandstone,  as  measured  in  the  apparatus  of  Fig.  99. 

333.  Relation  of  Pressure  to  Flow  Through  Sandstone. — 

When  the  flow  of  water  is  measured  through  sandstones 
such  as  constitute  most  water-bearing  beds  it  is  often  found 
that  here,  as  in  the  sands,  the  flow  may  increase  in  a  much 
higher  ratio  than  the  pressure.  Three  series  of  such  obser- 
vations are  plotted  in  Fig.  98,  and  the  apparatus  used  is 
shown  in  Fig.  99. 

Where  the'flow  does  not  increase  as  rapidly  as  the  pres- 
sure the  departure  from  the  theoretical  flow  has  been  ex- 
plained by  assuming  that  the  currents  become  turbulent 
and  thus  reduce  the  discharge;  but  no  satisfactory  reason 
has  yet  been  assigned  to  the  cases  where  the  flow  increases 
faster  than  the  pressure. 

334.  Observed  Hates  of  Flow  of  Water  Through  Sands  and 
Sandstones. — The  observed  rates  of  flow  of  water  throuHi 
the  series  of  sands  represented  in  Fig.  96,  when  expressed 


Flow  of  Ground  Water. 


269 


in  cubic  feet  per  minute  per  square  foot  of  section  and  per 
foot  of  length,  under  a  gradient  of  1  in  10,  is  given  below: 


No.  8         7  6  5l/j  5 

Cn.  ft.  per  min.    5.23       3.65       1.85       1.36       1.22 


4 

.82 


3 
.51 


210 
.33      .23      .18 


Fio.  99.— Apparatus  for  measuring  the  flow  of  water  through  sandstones, 
under  different  known  pressures. 


According  to  Darcy's  law,  if  these  sand  columns  had  their 
lengths  increased  10,  100  and  1,000  times  the  discharges 
observed  would  be  only  A,  TOTT  and  ToW  of  those  given. 
In  the  case  of  four  sandstones  the  rates  of  flow  were  so  slow 
that  10  days  were  required  for  .29,  .34,  2.45  and  .14  cubic 


270       Ground  Water,  Wells,  and  Farm  Drainage 

feet  of  water  to  be  discharged  under  the  conditions  for  the 
eand. 

335.  General  Movement  of  Ground  Water  Across  Wide 
Areas. — The  waters  which  supply  artesian  wells  and  many 
springs,  where  the  discharges  take  place  through  openings 
in  overlying  impervious  beds,  are  often  obliged  to  travel 
long  distances,  even  100  or  more  miles,  before  reaching 
their  outlets.     But  this  cannot  occur  with  such  low  rates  of 
flow  as  those  observed  in  (334)  and  it  is  clear  that  nearly 
the  whole  movement  across  long  distances  must  take  place 
through  rock  fissures  and  along  bedding  planes,  the  water 
seeping  out  of  the  rock  into  these  as  it  does  into  river  chan- 
nels and  lines  of  tile  drains. 

336.  Fluctuations  in  the  Rate  of  Flow  of  Ground  Water. — 
When  arrangements  are  made  to  automatically  record  the 
rate  of  discharge  of  water  from  springs,  artesian  wells  or 
lines  of  tile  drains  it  is  seen  that  the  flow  is  not  uniform, 
varying  not  only  with  the  season,  but  often  daily  and  even 
hourly. 


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Via.  100. — Showing  observed  barometric  changes  in  the  rate  of  flow  of 
water  from  a  spring,  and  the  apparatus  for  recording  it.  Lower  curve, 
record  of  spring. 

In  Fig.  100  is  shown  an  autographic  record  of  the  dis- 
charge of  water  from  a  spring  during  13  days,  together  with 
the  changes  in  barometric  pressure  as  recorded  by  a  baro- 
graph 45  miles  to  the  west  of  the  spring.  The  method  of 


Fluctuations  of  Ground  Water. 


271 


recording  the  changes  is  also  represented  in  the  same  figure. 
The  changes  in  the  rate  of  discharge  from  the  spring,  which 
are  associated  with  changes  in  the  pressure  of  the  atmos- 
phere, amount  to  as  much  as  8  per  cent,  of  the  total  nor- 
mal flow. 


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FIG.   101.— Showing  the   barometric   changes   in   the   rate   of   seepage   into 
tile  drains.    Lower  curve,  drain. 

337.  Barometric  Changes  in  the  Discharge  of  Water  from 
Tile  Drains. — Using  the  same  means  for  recording  the  rate 
of  discharge  of  water  from  tile  drains  it  was  shown  that 
changes  occur  here  which  are  entirely  analogous  to  those  re- 
corded from  the  spring,  and  Fig.  101  shows  a  week's  record 
of  the  changes  both  in  atmospheric  pressure  and  in  the  rate 
of  discharge  from  a  system  of  tile  drains.  In  this  system 
changes  in  the  rate  of  flow  as  great  as  15  per  cent,  of  the 
mean  have  been  recorded,  entirely  independent  of  rainfall 
and  apparently  due  solely  to  changes  in  atmospheric  pres- 
sure. 

338.  Diurnal  Changes  in  the 
Rate  of  Discharge  from  Tile 
Drains. — Besides  the  changes  as- 
sociated with  changes  of  baro- 
metric pressure  referred  to  in 
(337)  there  may  also  be  diurnal 
changes  in  the  rate  of  discharge 
which  are  due  to  the  diurnal 
changes  which  take  place  in  the 
soil  air  above  the  ground  water. 
As  the  air  expands  under  the  heat 
absorbed  it  presses  downward 
wePii«eVdue0fto'achlLges  Sinrfsoa  upon  the  water,causing  it  to  drain 
temperature.  away  faster,  which  makes  it 


7f-' 


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211 


272       Ground  Water,  Wells  and  Farm  Drainage. 


much  as  if  a  rain  had  occurred  and  percolation  had  in- 
creased the  hight  of  the  ground  water  itself.  Fig.  102 
shows  the  changes  which  did  occur  in  the  level  of  the  water 
in  surface  wells  near  the  system  of  tile  drains  in  question. 
The  curves  were  produced  at  the  same  time  by  self-record- 
ing instruments.  Fig.  103  shows  another  series  of  diurnal 
fluctuations  where  the  changes  in  level  were  measured 
twice  daily,  in  the  morning  and  at  night,  and  Fig.  104 
shows  the  conditions  under  which  these  changes  occurred. 
The  lower  curve  represents  the  changes  in  the  inner  well 
while  the  upper  curve  shows  those  in  the  outer  well  where 
the  water  percolated  from  above  the  stratum  of  clay  under 
the  influence  of  the  air  pressure  caused  by  the  diurnal 
changes  in  temperature. 


FIG.  103.—  Showing  diurnal  changes  in  the  FIG.  101.-  Sh..»  M.K  the  soil  con- 
level  of  the  ground  water  measured  twice  ditions  under  which  the  changes 
daily  in  surface  wells.  of  Fig.  103  took  place. 

339.  Fluctuations  in  the  Level  of  Water  in  Wells. — In  all 
ordinary  wells,  whether  they  are  deep  or  shallow,  the  water 
is  seldom  at  rest,  the  surface  continually  either  rising  or 
falling  through  varying  distances,  and  Fig.  105  is  a  record 
of  one  such  series  of  changes  which  it  will  be  seen  are  nearly 


Fluctuations  of  Ground  Water. 


Wednesday  prfjhursday  Friday 

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FIG.  l<55.— Showing  fluctuations  in  the  level  of  water  in  a  well  and  simul- 
taneous fluctuations  iu  the  rate  of  discharge  from  a  spring  half  a  mile 
distant. 


FIG.  106.— Showing  sudden  and  large  fluctuations  in  the  level  of  water 
in  a  well,  during  times  of  thunder  showers,  due  to  sudden  changes  in 
pressure. 


274       Ground  Water,  Wells  and  Farm  Drainage. 

coincident  in  phase  with  those  which  occurred  in  the  dis- 
charge of  water  from  a  spring.  Changes  much  more  vio- 
lent than  these  and  of  shorter  duration  are  shown  in  Fig. 
106.  Fluctuations  like  these  occur  at  times  of  violent 
thunder  storms  and  are  due  to  changes  in  air  pressure  and 
not  to  rainfall.  In  this  case  the  changes  occurred  in  :i 
drilled  well  60  feet  deep  with  6  inch  steel  casing  to  rock 
and  the  changes  in  the  level  of  the  water  were  so  great  that 
the  instrument  had  to  be  set  over  three  times  to  keep  the 
pen  on  the  record  sheet. 


CHAPTER  XIII. 

FARM  WELLS. 

340.  Essential  Features  of  a  Good  Well. — The   essential 
features  of  a  good  well  are :   (1)   Ample  capacity  to  supply 
pure,  clear,  cold  water.   (2)  A  location  which  renders  it  not 
likely  to  be  contaminated  by  seepage  from  surface  impuri- 
ties.    (3)  A  casing  or  curbing  which  is  vermin  proof  at 
the  top  and  if  possible  water-proof  in  its  upper  10  to  20  feet. 

341.  The  Capacity  of  a  Well — The  capacity  of  a  well 
should  always,  if  possible,  be  much  greater  than  the  prob- 
able demands  which  will  be  put  upon  it,  and  it  should  not 
be  possible  in  a  few  hours  to  pump  it  dry  with  an  ordinary 
pump. 

In  working  the  ordinary  domestic  pump  about  20  strokes 
are  made  per  minute  and  these  will  fill  a  pail  with  20  to  24 
pounds;  this  is  at  the  rate  of  about  a  cubic  foot  or  7.5  gal- 
lons in  3  minutes  and  a  good  well  should  be  able  \  o  supply 
water  at  this  rate  for  several  hours  without  failing. 

The  domestic  animals  on  the  farm  will  need  water  at  the 
rate  of  more  rather  than  less  than  a  cubic  foot  per  each 
1,000  Ibs.  of  weight  per  day.  A  cow  giving  a  heavy  flow  of 
milk  often  takes  nearly  2  cubic  feet  of  waiter  in  24  hours. 

Five  cows,  during  120  days  in  winter,  averaged  85.4  Ibs. 
per  head  when  the  water  was  warm  and  77.3  Ibs.  when  it 
was  cold.  At  this  rate  the  equivalent  of  40  adult  cows 
would  need  3,416  Ibs.  of  water  or  54.7  cubic  feet  and  this 
would  require,  at  the  rate  assumed  above  for  pumping,  2 
hours  and  45  minutes  to  supply  them. 


276         Ground  Water,  Wells  and  Farm  Drainage.    '  ' 

342.  Geological  Conditions  Which  Give  the  Best  Wells 

The  largest  and  best  supplies  of  well  water  are  usually  found 
in  the  extensive  sandstone  formations  and  wherever  these 
are  within  easy  reach  the  well  should  be  sunk  into  them 
deep  enough  to  have  20  or  more  feet  of  percolating  sand- 
stone surface.  Next  to  the  sandstone  formations  as  sources 
of  water  supply  stand  the  fissured  limestones  which  either 
overlie  sandstones  or  are  so  related  to  the  surface  soil  that 
water  from  them  can  percolate  down  into  the  fissures  and 
through  them  reach  the  well  when  sunk  so  as  to  connect 
with  a  system  of  these  fissures. 

Again  beds  of  sand  between  beds  of  clay  often  give  large 
supplies  of  pure  cold  water. 

In  many  localities  artesian  or  flowing  wells  can  be  se- 
cured and  some  of  the  conditions  under  which  these  origi- 
nate are  represented  in  Fig.  107. 

343.  Conditions  which  Influence  the  Capacity  of  a  Well.— 
The  rate  at  which  water  can  enter  a  well  depends  upon  five 
prime  factors:     (1)   The  size  of  the  grains  of  the  water- 
bearing beds  and  the  pore  space.     (2)   The  depth  of  the 
well  in  the  water-bearing  bed.     (3)   The  amount  the  water 
is  lowered  in  the  well  when  pumping.     (4)  The  diameter 
of  the  well.     (5)  Whether  the  well  is  in  or  near  a  system 
of  fissures. 

344.  Influence  of  Size  of  Grains  and  Fore  Space  on  the 
Capacity  of  the  Well. — From  the  fact  that  the  flow  of  water 
through  sands  is  nearly  proportional  to  the  squares  of  the 
diameters  of  the  soil  grains,  and  is  greater  the  larger  the 
pore  space,  it  is  clear  that  these  are  very  important  factors 
in  determining  the  capacity  of  wells.  It  has  been  computed 
that  when  all  other  factors  are  the  same  the  capacities  of 
two  wells,  in  sands  having  the  diameter  of  grains  of  .15 
mm.  and  .25  mm.  and  pore  spaces  of  30  per  cent,  and  32 
per  cent.,  are  to  each  other  as  5.234  to  18.01  or  one  is  over 
three  times  the  other.      It  is  therefore  clear  that  when  the 
sand  grains  and  pore  space  are  small  the  other  well  factors 
must  be  made  enough  larger  to  compensate. 


Capacity  of  Wells. 


277 


KetftfKtmge 


FIG.  107. — Showing  geological  conditions  under  which  artesian  wells  are 

formed. 

18 


278       Ground  Water,  Wells  and  Farm  Drainage. 


The  capacity  of  a  6-inch  well  sunk  100  feet  into  sand- 
stone having  different  sizes  of  sand  grains  but  with  uni- 
form pore  space  of  32  per  cent,  and  a  temperature  of  50° 
F.  give  computed  flows  under  a  pressure  of  four  feet  as 
follows : 


Size  of  grains  in  m.  m. 

.02 

.01 

.06 

.08 

.1 

.2 

.4 

.6 

Cu.  ft  per  min  

.047 

.189 

.580 

.757 

1.0S3 

4.73 

18.93 

57.% 

345.  Influence  of  Depth  on  the  Capacity  of  a  Well. — When 
other  conditions  are  the  same  the  greater  the  depth  of  a 
well  in  the  water-bearing  beds  the  greater  will  be  its  capac- 
ity because  this  increases  the  area  of  the  section  of  the 
sand  or  sandstone  through  which  the  water  may  enter  the 
well. 

If  a  6-inch  well  is  sunk  just  to  the  surface  of  a  water- 
bearing bed  the  area  through  which  the  water  can  enter  it  is 
only  28.27  square  inches.  So,  too,  if  a  6-inch  well  casing 
ends  in  a  water-bearing  sand  only  so  much  water  can  enter 
this  well  as  can  flow  through  a  circle  of  sand  6  inches  in 
diameter. 

If  the  well  penetrates  the  water-bearing  bed  one  foot  so 
that  water  can  enter  the  sides  as  freely  as  it  enters  the  bot- 
tom then  the  percolation  surface  will  be  increased  to 

28.27  +  226.2  -  254.47  sq.  in. 

making  the  section  of  flow  nine  times  as  great.  Leaving 
the  bottom  of  the  well  out  of  consideration  it  is  clear  that 
doubling  the  depth  of  the  well  in  the  water-bearing  beds 
doubles  the  area  for  water  to  enter  and  hence  it  is  a  matter 
of  the  greatest  importance  to  secure  a  sufficiently  large  per- 
colating surface  in  the  water-bearing  beds.  This  capacity 
increases  in  a  somewhat  slower  ratio  than  the  depth,  as  in- 
dicated in  the  table  below, 


Capacity  of  Wells. 


279 


Table  showing  the  flow  in  a  6-inch  well  sunk  different  depths 
into  200  feet  of  water-bearing  sandstone  where  the  pore  space 
is  32  per  cent,  and  the  diameter  of  the  grains  .25  m.  m. 


Flow  in  cubic  feet  per 

Depth  of  well  in  feet. 

4. 

8. 

12. 

16. 

20. 

40. 

80. 

100. 

200. 

1.003 

1.818 

2.544 

3.265 

4.08 

7.68 

14.88 

18.49 

36.02 

346.  Influence  of  Pressure  on  the  Capacity  of  a  Well. — 

Since  the  flow  of  water  through  sands  and  sandstone  is  some- 
what nearly  proportional  to  the  effective  pressure  it  is  clear 
that  the  depth  of  water  in  the  well  at  low  water  stage  should 
be  great  enough  to  permit  its  surface  to  be  lowered  until  the 
needed  pressure  to  force  the  water  into  the  well  is  de- 
veloped. 

If,  in  pumping,  the  water  in  a  well  is  lowered  4  feet  the 
pressure  developed  will  be  about  that  of  four  feet  of  water 
and  to  lower  it  8,  12,  16  or  20  feet  will  increase  the  pres- 
sure 2,  3,  4  and  5-fold.  This  relation  being  true  it  is  clear 
that  not  only  should  there  be  an  ample  depth  of  water  in  the 
well  but  the  cylinder  of  the  pump  should  be  so  placed  as  to 
enable  the  full  depth  to  be  utilized. 

In  the  case  of  a  6-inch  well  sunk  100  feet  into  water- 
bearing sandstone  200  feet  thick  having  a  pore  space  of  32 
per  cent,  and  diameter  of  grains  of  .25  mm.  the  capacity 
of  the  well  under  different  pressures  is  computed  to  be  as 
follows: 

Amount  the  water  is  lowered  in  the  well  in  pumping. 


Cu.  ft.  per  minute  

1 

1.8483 

2 

3.6966 

4 

7.3932 

8 
14.7864 

12 

22.1796 

16 

29.5728 

20 
36.966 

347.  Influence  of  the  Diameter  of  the  Well  on  its  Ca- 
pacity.— The  capacity  of  wells  when  they  extend  any  con- 
siderable depth  into  the  water-bearing  beds  does  not  in- 
crease as  rapidly  with  increase  of  diameter  as  might  be  ex- 


280       Ground  Water,  Wells  and  Farm  Drainage. 


peeted,  and  Slichter  computes  that  three  wells  2  inches,  6 
inches  and  12  inches  in  diameter  respectively,  if  sunk  100 
feet  into  a  bed  of  sandstone  having  sand  grains  .25  mm.  in 
diameter  and  a  pore  space  of  32  per  cent,  will  have  capaci- 
ties in  cubic  feet  per  minute  as  follows,  when  the  water  is 
lowered  20  feet: 

Diameter.  Diameter.  Diameter. 

2  inch.  6  inch.  12  inch. 

Cubic  ft.  per  minute ....  31 . 90  36 . 94  44 . 45 

These  amounts  are  on  the  assumption  that  the  walls  of 
the  well  or  casing1  offer  no  resistance  to  the  discharge, 
which  of  course  is  not  true,  and  the  2-inch  well  could  not 
discharge  the  amount  indicated  under  the  pressure  of  20 
feet  although  that  amount  could  enter  the  well  if  it  were 
removed  fast  enough. 


FIG.  108.— Shows  a  good  form  of  sand  strainer  made  by  sawing  slots  in 

brass  tubing. 

It  is  clear  from  these  results  that  for  most  wells  there  is 
little  gained  in  making  them  larger  in  diameter  than  is 
needed  to  provide  accommodation  for  the  pump. 


Capacity  of  Wells. 


281 


348.  The  Use  of  Sand  Strainers — Where  water  must  be 
procured  in  loose  sand,  especially  if  it  is  fine,  some  form  of 
sand  strainer  should  be  used  unless  the  well  is  an  open  one 
and  even  then  a  suitable  point  will  often  greatly  increase 
the  capacity. 

The  difficulty  in  getting  water  rapidly  from  loose  sand 
grows  out  of  its  tendency  to  move  with  the  water,  filling  up 
the  well  or  the  suction  pipe  or  cutting  out  the  valves.  Since 
the  specific  gravity  of  sand  is  only  about  2.65  just  as  soon 
as  a  pressure  greater  than  3  feet  is  developed  to  force  the 
water  out  of  the  sand  the  sand  must  move  with  it  unless 
there  is  something  to  prevent  it. 


FIG.  109.— Showing  ordinary  sand  strainers  and  method  of  measuring  their 

capacity. 

The  best  sand  strainer  we  have  seen  is  represented  in  Fig. 
108  and  is  made  of  heavy  brass  tubing  cut  as  shown  in  the 
illustration,  the  width  of  the  cuts  varying  for  the  different 
degrees  of  fineness  of  sand.  Made  of  heavy  stock  and  of 
one  kind  of  metal  it  is  not  liable  to  corrode  and  clog  as  with 
the  common  form  represented  in  Fig.  109. 

349.  Capacity  of  Sand  Strainers — The  capacity  of  sand 
strainers  varies  essentially  in  the  same  way  as  wells  of  simi- 
lar dimensions  would,  made  in  the  same  kind  of  material. 
The  longer  the  strainer,  the  coarser  the  sand  and  the  greater 
tlie  pressure  the  larger  will  be  the  capacity. 


282       Ground  Water,  Wells  and  Farm  Drainage. 

In  Fig.  109  is  represented  a  method  used  in  measuring 
the  capacity  of  three  Gould  Sand  Strainers,  Nos.  50,  80 
and  90,  each  18  inches  long,  and  the  table  below  gives  the 
results  secured. 

Table  showing  the  rate  of  flow  through  three  drive  well  points. 


Pressure 

No.  50. 

No.  80. 

No.  90      ' 

feet. 

Lbs.  per  in  in. 

Lbs.  per  min. 

Lbs.  per  min. 

2 

6.6 

2.2 

.57 

4 

13.2 

4.4 

1.14 

6 

19.8 

6.6 

1.72 

8 

26.4 

8.8 

2.29 

10 

33.0 

11  0 

2.86 

12 

39.6 

13.2 

3.43 

14 

46.2 

15.4 

4.00 

16 

52.8 

17.6 

4.58 

18 

59.4 

19.8 

5.15 

20 

66.0 

22.0 

5.72 

The  sand  about  the  No.  50  strainer  had  a  diameter  of 
.294  mm.,  that  about  the  No.  80  .172  mm.,  and  about  the 
No.  90  .085  mm.  The  table  shows  under  these  conditions 
about  2  minutes  of  steady  flow,  under  a  pressure  of  12  feet, 
are  required  for  the  No.  50  strainer  to  supply  sufficient 
water  for  a  single  cow  one  day;  6  minutes  for  the  No.  80 
and  more  than  20  minutes  for  the  No.  90  strainer. 

It  would  tharefore  be  necessary  to  use  a  strainer  54 
inches  long  in  the  No.  80  sand  and  one  17  feet  long  in  the 
No.  90  sand  to  supply  the  water  obtained  through  the  No. 
50  strainer. 

350.  Capacity  of  a  Pump  on  a  Sand  Point  and  on  an  Open 
Suction  Pipe. — When  an  ordinary  pump  is  connected  up  in 
the  manner  represented  in  Fig.  110,  so  as  to  draw  water 
through  the  sand  point  or  through  the  open  suction,  the 
capacity  of  the  pump  under  the  two  conditions  may  be 
very  different.  In  the  case  of  a  two  and  a  half  inch  cylinder 
working  on  an  18  inch  No.  50  sand  strainer,  or  on  the  open 
suction  pipe  as  represented  in  the  illustration,  when  20 
strokes  would  fill  the  pail  from  the  open  suction  it  required 


Capacity  of  Wells. 


283 


35,  made  at  the  same  rate,  to  raise  the  same  amount  of 
water,  and  the  energy  required  to  do  the  work  v/as  much 
greater.  The  increased  labor  was  due  to  the  face  that  the 
water  came  in  too  slowly  through  the  sand  point  to  fill  the 
space  behind  the  piston  as  rapidly  as  it  was  raised  and  a 
vacuum  was  formed;  into  this  the  piston  fell  when  the  pres- 
sure was  released  and  the 
water  for  only  about  half  a 
stroke  could  be  secured. 

Sand  strainers  give  a  fair 
well  in  very  coarse  material 
where  one  of  sufficient  size 
can  be  placed  in  a  water- 
bearing bed  of  sufficient 
thickness,  but  generally  they 
can  be  depended  upon  for 
only  small  amounts  of 
water.  For  wind-mill  ser- 
vice they  are  less  satisfac- 
tory because  of  the  greater 
power  required  to  work  the 
pump. 

351.  Depth  of  the  Well  __ 
An  important  feature  of 
every  well,  where  the  water 
is  intended  for  domestic  or 
stock  use,  is  a  sufficient 
depth  to  prevent  the  quick 
entrance  of  water  from  the 
surface  and  to  maintain  a 
constant  low  temperature. 
This  depth  should  usually 
exceed  20  feet  and  even 
where  water  is  found  nearer 
the  surface  than  this  it  is 
better,  if  the  water-bearing 

l^/Ir,  -.-.^ll  ^      ™*.».  ^-C  It-    4-^    -.^ 
beds  Will  permit  OI  it,  tO  gO 

30    Or    more    feet    and    then 


'  HO.—  Showine  method  of  comparing 
the  capacity  of  a  pump  working  on 
sand  strainer  and  on  an  open  well 


284       Ground  Water,  Wells  and  Farm  Drainage. 

place  the  pump  so  as  to  draw  the  water  from  the  bottom 
where  it  is  coolest  and  freshest. 

Both  depth  of  soil,  to  act  as  a  filter,  and  time  to  bring 
about  changes  in  surface  waters,  to  free  them  from  organic 
matter,  are  required  in  order  to  render  the  water  falling 
upon  the  ground  pure  and  suitable  to  drink. 

352.  Temperature  of  Well  Water — The  zone  of  lowest 
ground  temperature  is  generally  from  20  to  70  feet  below 
the  surface  and  in  this  zone  the  coldest  waters  are  pro- 
cured.    Above  20  feet  the  waters  will  be  colder  in  winter 
and  warmer  in  summer  and  below  70  to  75  feet  the  water 
generally  becomes  warmer  from  the  internal  heat  of  the 
earth. 

The  normal  temperature  of  the  coldest  well  water  in  a 
locality  is  usually  from  2  to  4  degrees  higher  than  the  mean 
annual  air  temperature  of  the  place,  and  in  Wisconsin  this 
ranges  from  43°  in  the  northern  portion  to  about  50°  in 
the  southern  portion. 

353.  Well  Casing  or  Curbing — Everything     considered 
there  is  probably  nothing  better  for  a  curbing  or  casing  for 
a  well  than  the  6  inch  lap-weld  steam  pipe.  The  same  pipe 
galvanized  is  better  because  it  will  not  rust  out  so  quickly. 
The  great  advantage  of  this  kind  of  casing  is  that  it  is  so 
completely  water  tight  and  at  the  top  can  be  so  securely 
closed  as  to  prevent  insects  and  vermin  falling  in. 

Next  to  the  steel  casing  is  one  made  of  cement  tile  or 
glazed  sewer  tile  with  their  joints  set  in  cement.  Where  a 
well  is  to  have  a  brick  or  stone  curbing  the  upper  10  feet 
should  be  laid  in  cement  and  plastered  with  the  same  on  the 
back  to  exclude  surface  water  and  vermin. 

354.  Top  of  the  Well — In  finishing  a  well  the  casing 
should  be  carried  12  to  18  inches  above  the  surrounding 
surface  and  then  earth  be  graded  up  to  it  so  as  to  secure  per- 
fect and  quick  removal  of  all  surface  water. 


Well  Casing  and  Curling.  285 

Where  a  steel  casing  is  used  the  well  platform  is  best 
made  bj>  screwing  a  wide  flange  on  the  top  and  then  bolting 
the  pumphead  directly  to  this,  having  first  drilled  holes 
through  both  to  receive  the  bolts.  This  arrangement  secures 
a  very  solid  and  perfectly  tight  platform.  Around  this 
plank  may  be  laid,  or  better  still,  a  block  of  cement. 


CHAPTER  XIV. 
PRINCIPLES  OF  FARM  DRAINAGE. 

Both  irrigation  and  drainage  are  usually  looked  upon  as 
arts  whose  application  to  agriculture  are  required  only  in 
special  cases;  but  a  broader  and  more  helpful  conception  is 
that  all  fertile  fields  must  be  both  well  irrigated  and  thor- 
oughly drained. 

It  is  true  that  over  much  the  larger  portion  of  the  earth's 
surface  the  water  required  for  the  growth  of  crops  is  sup- 
plied by  the  natural  rainfall,  and  when  this  is  timely  and 
sufficient  it  is  the  best  and  ideal  irrigation,  done  by  nature's 
hand. 

It  is  again  fortunately  true  that  most  land  areas  have  ac- 
quired such  surface  features  that  the  excess  of  rainfall  is 
opportunely  removed  by  percolation  and  seepage  or  surface 
flow;  and  this  is  nature's  method  of  land  drainage. 

The  fundamental  fact  is  that  all  lands  must  be  irrigated 
or  watered  and  drained  and  in  special  cases  nature's  efforts 
need  to  be  supplemented. 

355.  Necessity  for  Drainage. — There  are  several  impera- 
tive demands  for  the  drainage  of  farm  lands: 

1.  The  removal  of  the  more  soluble  salts  formed  by  the 
decay  of  rock  and  organic  matters,  because  when  the  soil 
water  becomes  too  strong  in  soluble  salts  it  either  poisons 
the  plant  or  renders  the  root  hairs  inactive  by  causing  them 
to  shrivel.     If  these  soluble  salts  which  plants  cannot  use 
are  not  removed  the  soil  comes  into  the  condition  known 
as  alkali  lands,  upon  which  little  vegetation  can  grow. 

2.  The  water  in  the  soil  needs  to  be  frequently  changed 
or  replaced  by  a  fresh  supply  containing  an  abundance  of 


•'   .       Conditions  Requiring  Drainage.  287 

atmospheric  oxygen  because  the  roots  of  plants  and  micro- 
scopic life  tend  to  exhaust  this  supply.  If  the  soil  is  not 
drained  "the  water  in  it  becomes  stagnant  in  a  sense,  the 
rains  which  fall  simply  running  off  the  surface,  leaving  the 
soil  water  the  same  as  was  there  before  the  rain. 

3.  Farm  lands  must  be  drained  in  order  to  render  them 
sufficiently  firm  to  permit  the  farm  operations. 

4.  Soils  must  be  drained  in  order  to  provide  room  for 
soil  air.     (238.)      (251.) 

5.  The  excess  of  water  must  be  removed  to  permit  the 
soil  to  become  warm  enough  for  plant  growth.       (268.) 
(271.) 

356.  Conditions  which  Require  Drainage — The  cases  in 
which  it  becomes  desirable  to  supplement  natural  drainage 
fall  into  five  classes: 

1.  Comparatively  flat  lands  or  basins  upon  which  the 
water  from  the  surrounding  higher  lands  collect. 

2.  Areas  adjacent  to  higher  lands  where  the  structure  is 
such  as  to  permit  the  water  which  sinks  into  the  high  land 
to  flow  or  seep  under  and  up  through  the  low  ground, 
making  them  wet. 

3.  Lands  inundated  regularly  by  the  rise  of  tides  or  fre- 
quently by  the  overflow  of  rivers. 

4.  Extremely  flat  lands  in  wide  areas  which  are  under- 
laid near  the  surface  by  a  thick,  close,  nearly  impervious 
stratum  of  clay,  such  as  were  formerly  old  lake  bottoms. 

5.  Lands  like  rice-fields,  water-meadows  and  cranberry 
marshes  where  water  is  applied  in  excessive  quantities  at 
stated  times  and  must  be  removed  again  quickly. 

357.  Deep  Drainage  Increases  Root  Room. — No  plant  can 
utilize  the  resources  of  the  soil  to  the  best  advantage  unless 
there  is  provided  for  it  an  abundance  of  root  room.    In  all 
well  drained  soils  the  roots  of  most  cultivated  crops  spread 
themselves  widely  and  to  a  depth  of  2.5  to  4  or  more  feet. 
When  conditions  are  such  as  to  permit  crops  to  do  this  the 
beet  growth  and  largest  yields  result. 


288       Ground  Water,  Wells  and  Farm  Drainage. 

Proper  drainage  so  lowers  the  ground  water  surface  that 
roots  are  able  to  penetrate  to  their  normal  depth,  and  Fig. 
Ill  shows  how  the  roots  of  corn  have  been  massed  together 
near  the  surface  because  of  too  much  water  in  the  soil  be- 
low, and  Fig.  45,  p.  147,  shows  the  apparatus  with  the  corn 
growing  in  it. 

358.  Drainage  Increases  the  Available  Moisture. — When 
the  roots  of  a  crop  are  forced  to  develop  so  close  to  the  sur- 
face as  shown  in  (357)  the  first  effect  is  to  exhaust  the  soil 
of  its  moisture  so  much  as  to  leave  it  too  dry  and  so  lessen 
the  capillary  rise  that,  although  there  is  an  abundance  of 
water  in  the  soil  below,  it  cannot  be  brought  to  the  roots 
and  the  soil  below  is  too  wet  to  permit  the  roots  to  go  to 
the  moistura 

OB  the  other  hand  if  the  ground  water  is  lowered  the 
roots  are  permitted  to  advance  deeper,  making  it  unneces- 
sary for  the  water  to  move  up  as  high  and  leaving  the  soil 
more  moist,  and  so  capillary  action  stronger  and  capable  of 
lifting  water  higher  and  faster.  (198.)  (199.) 

359.  Soil  Made  Warmer  by  Drainage. — Whenever  soils 
are  kept  continuously  wet,  so  that  large  amounts  of  water 
evaporate  from  their  surfaces,  the  temperature  is  low.  Two 
thermometers  having  their  bulbs  side  by  side,  one  left  naked 
and  the  other  covered  with  a  close  fitting  layer  of  wet  mus- 
lin, will  often  show  temperatures  as  much  as  20°  different, 
the  wet  one  colder,  made  so  by  the  evaporation  of  water. 
The  teakettle  on  the  stove  has  the  temperature  of  its  bottom 
held  constantly  near  212°  by  the  evaporation  of  the  boil- 
ing water,  showing  the  cooling  power  of  water  when  evapo- 
rating. 

During  early  spring  differences  in  soil  temperature  at  the 
surface,  due  to  differences  in  drainage,  may  often  be  as 
great  as  12°. 

The  differences  in  the  amount  of  moisture  in  clayey  and 
sandy  soil  often  cause  a  difference  of  7°  F.,  in  the  surface 


CoriSUions  Requiring  Drainage,  2.8.9 


PIG.  111.— Showing  how  the  roots  of  corn  are  forced  to  develop  near  the 
surface  when  the  soil  i«  not  drained.    See  apparatus,  Fig.  45,  p   147 


290       Ground  Water,  Wells  and  Farm  Drainage. 

foot,  when  both  are  well  drained,  and  as  much  as  5°  in  the 
second  and  third  feet. 

360.  Soil  Better  Ventilated  by  Drainage — The  change  of 
air  in  wet  soils  after  they  have  been  well  drained  is  very 
much  more  thorough  and  this  is  perhaps  the  greatest  bene- 
fit due  to  drainage. 

There  are  several  ways  in  which  thorough  drainage  leads 
to  a  more  rapid  exchange  of  air  in  the  soil: 

1.  Lowering  the  ground  water  enables  both  the  roots  of 
plants,  and  animals  like  earthworms  and  ants,  to  penetrate 
the  soil  more  deeply,  leaving  passageways  larger  and  freer 
than  existed  before. 

2.  When    the    deeper    clays    come  to  dry  after  being 
drained  shrinkage  checks  are  formed  in  great  numbers  and 
through  these  the  air  moves  more  freely. 

3.  With  the  deeper  penetration  of  soil  air  nitrates  are 
more  freely  formed,  and  with  the  larger  amounts  of  soluble 
salts  the  clay  is  flocculated,  making  a  more  granular  text- 
ure, which  again  admits  the  air  more  freely. 

4.  When  lines  of  tile  are  laid  under  a  field  50  to  100  feet 
apart  they  furnish  an  opportunity,  with  every  change  in 
atmospheric  pressure  and  of  soil  temperature,  to  force  air 
into  and  out  of  the  soil,  and  so  a  line  of  tile  laid  in  the  soil 
becomes  a  system  for  air  circulation. 

5.  With    every    heavy     rain  which  causes  percolation, 
where  the  water  can  flow  away,  a  volume  of  fresh  air  is 
drawn  into  the  soil  after  it,  completely  changing  the  air. 

361.  Kinds  of  Drains. — There   are  two  types   of  drains: 
(1)  closed  and  beneath  the  surface  after  the  manner  of  un- 
derground water  channels;  and  (2)  open,  such  as  ditches, 
which  are  in  function  like  natural  river  channels. 

The  closed  forms  are  usually  most  effective,  least  in  the 
way,  require  less  expense  in  maintenance  and  are  most 
durable  and  should  generally  be  adopted,  but  there  are  cases 
where  surface  ditches  must  be  used. 

Jn  the  earlier  history  of  underdraining  closed  drains  were 


Kinds  of  Drains.  291 

made  by  laying  bundles  of  twigs  in  the  bottom  of  the  ditch 
and  covering  them,  expecting  the  water  to  trickle  through 
the  passageways  left.  In  other  cases  two  or  three  round 
poles  were  covered  in  the  bottom,  of  the  ditch  or  two  slabs 
were  laid  edge  to  edge  with  their  round  sides  down.  Two 
boards  were  sometimes  set  on  edge  V-shaped,  with  opening 
down. 

More  permanent  closed  drains  were  made  by  filling  the 
bottom  of  the  ditch  with  cobblestone,  by  setting  flat  stone 
on  edge  V-shape,  by  setting  two  lines  of  stone  on  edge  and 
covering  with  flat  stone  and  even  by  using  four  stone  for 
top,  bottom  and  sides.  In  other  cases  brick  were  used  in 
place  of  stone  and  some  even  made  tile  out  of  blocks  of  peat, 
cutting  semi-cylindrical  cavities  in  the  faces  of  square 
blocks  of  peat,  then  laying  these  together  to  form  the  water- 
way. Most  of  these  devices,  however,  must  be  looked  upon 
as  makeshifts  rather  than  as  permanent  improvements,  and 
have  largely  gone  out  of  use. 

The  modern  tile,  made  of  hard  burned  clay,  is  cylindrical 
in  form  and  usually  in  1-foot  lengths  with  diameters  rang- 
ing from  2  to  12  or  more  inches. 

362.  Essential  Features  of  Drain  Tile — A  good  drain  tile 
should  be  hard  burned,  giving  a  clear  ring  when  struck. 
It  is  much  more  important  to  have  them  hard  burned  and 
strong  than  it  is  to  have  them  open  and  porous.  Soft 
burned  tile  which  give  little  or  no  ring  when  struck  are 
much  more  liable  to  crumble  down  under  the  action  of 
frost.  "We  have  visited  one  field  drained  with  soft  burned 
tile  laid  2.5  to  3.5  feet  deep  and,  in  less  than  five  years  after 
laying,  holes  appeared  in  the  field  in  many  places.  On 
digging  in  these  places  it  was  found  that  the  tile  had 
crumbled  into  small  chips,  caused  by  freezing. 

Tile  are  sometimes  made  from  clay  containing  pebbles 
of  limestone  which  when  burned  are  converted  into  lime. 
These  lumps  of  lime  bedded  in  the  tile  slack  as  soon  as 
epoujgh  reaches  theni  and  by  their  expansion  the  tjle 


292       Ground  Water,  Wells  and  Farm  Drainage. 

are  broken.    It  will  often  happen  that  such  tile  may  be  laid 
in  place  and  covered  before  the  slacking  occurs. 

Besides  being  hard  burned,  strong,  giving  a  clear  ring 
when  struck  and  free  from  lime  the  tile  should  be  smooth 
and  straight,  with  square  cut  ends  and  true  circular  outline 
so  that  they  may  be  laid  with  close  joints  which  will  ex- 
clude silt, 

363.  How  Water  Enters  Tile — The  texture  of  a  tile  is  like 
that  of  common  brick  and  will  allow  water  to  flow  readily 
through  the  walls,  but  even  were  the  walls  water  tight  the 
water  could  still  find  access  to  the  tile  through  the  joints 
formed  by  the  abutting  sections  as  rapidly  as  it  can  be 
brought  by  ordinary  soils  requiring  drainage. 

Measurements  made  of  the  rate  of  percolation  through 
2-inch  Jefferson,  Wisconsin,  tile  showed  a  flow  of  8. 1  cubic 
feet  per  100  feet  of  length  in  24  hours,  under  a  pressure  of 
23.5  inches,  when  surrounded  by  clear  water  only.  When 
the  same  tile  were  bedded  in  a  fine  clay  loam,  so  that  the 
water  had  to  percolate  through  the  soil,  the  discharge  was 
reduced  to  1.62  cubic  feet  per  24  hours  and  per  100  feet, 

364.  The  Use  of  Collars. — It   has    sometimes   been   the 
custom  to  use  collars  to  slip  over  the  joints  formed  by  the 
meeting  of  the  sections  of  the  tile,  with  the  idea  of  better 
excluding  the  silt  and  of  holding  a  better  alignment.     The 
collars  are  short  sections  of  a  size  of  the  tile  large  enough 
to  slip  over  the  joints  readily. 

The  use  of  collars  is  not  advisable,  first,  on  account  of  the 
greater  cost,  and  second,  because  when  good  tile  are  prop- 
erly laid  they  are  not  needed. 

365.  Depth  at  which  Drains  Should  be  Laid. — It  is  seldom 
necessary  to  lower  the  ground  water  more  than  four  feet 
below  the  surface  and  except  in  very  springy  places  a  depth 
of  3  feet  will  answer  most  purposes. 

Since  the  level  of  the  ground  water  changes  with  the 
season  and  since  many  lands  which  are  benefited  by  drain- 


Depth  of  Drains. 


293 


age  are  only  too  wet  during  the  spring  it  may  be  best 
to  lay  the  drains  only  so  deep  as  is  needful  to  bring 
the  field  into  condition  for  working  in  due  season, 
and  in  such  cases  tile  placed  2.5  to  3  feet,  rather  than  3.5 
to  4  feet,  will  usually  be  found  sufficient  for  general  farm 
crops. 

When  tile  are  placed  needlessly  deep  not  only  is  the  cost 
greater  but,  in  all  of  those  cases  where  there  is  an  under- 
flow of  water  from  the  higher  land,  the  level  of  the  ground 
water  is  drawn  down  earlier  in  the  season  to  such  a  depth 
that  the  crop  will  get  less  advantage  by  the  subirrigation 
resulting  from  the  capillary  rise  of  the  underflowing  water 
into  the  root  zone. 


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FIG.  112.— Representing  an  apparatus  for  demonstrating  the  slope  of  the 
ground  water  surface  back  from  a  tile  drain  and  the  changes  in 
pressure  when  discharge  is  taking  place.  A.  front  elevation  of  tank, 

with  a,   h,  c,  d,  faucets  from  drain  tile,  and  1,  2,  3,   15,  pressure 

gauges;  B,  B,  vertical  sections  lengthwise,  with  1,  2,  3,  4,  tile  and 
faucets,  and  5,  supply  tile  at  end;  C,  cross-section,  with  1,  2,  tile; 
D,  section  at  1  in  B,  showing  connection  of  faucet  with  tile. 

366.  Rise  of  Ground  Water  Away  from  Drainage  Outlet 

If  reference  is  made  to  the  contour  map  of  the  ground 
water  surface,  Fig.  89,  p.  257,  it  will  be  easy  to  compute 
19 


294       Ground  Water,  Wells  and  Farm  Drainage. 

the  gradient  of  the  ground  water  surface  as  it  rises  back 
from  the  lake.  In  well  29,  150  feet  from  the  lake,  the 
water  stood  on  a  certain  date  Y.214  feet  above  the  level  of 
the  water  in  the  lake,  thus  showing  a  mean  rise  or  .gradient 
of  1  foot  in  20.79  feet.  In  the  same  locality,  but  outside  the 
area  represented  by  the  map,  a  well  stands  1,250  feet  back 
from  the  lake  and  in  this  the  water  has  a  level  52  feet  above 
the  lake  or  drainage  outlet,  which  gives  a  mean,  gradient 
or  rise  of  1  foot  in  24.4. 

In  Fig.  112  is  represented  an  apparatus  for  demonstrat- 
ing the  position  of  the  surface  of  the  ground  water  and  the 
difference  of  pressure  at  different  distances  away  from  and 
above  a  drain  tile,  and  Fig.  113  shows  the  observed  differ- 
ences of  pressure  under  two  sets  of  conditions. 

In  Fig.  114  is  also  represented  the  general  slope  of  the 
ground  water  surface  and  the  modification  of  it  by  a  line 


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FIG.  113.— Showing  the  changes  in  pressure  at  different  distances  fri.m 
the  tile  drain  when  the  water  is  flowing.  The  lower  curve  shows  (lie 
pressure  when  the  flow  is  from  the  stopcock  a.  Fig.  112,  and  (lie 
upper  set  of  curves  represent  changes  which  occurred  during  a  period 
of  flow  from  the  stopcock  c,  Fig.  112. 

of  infiltration  pipes,  which  is  in  effect  a  tile  drain.  The 
rate  of  rise  of  the  ground  water  back  from  a  tile  drain  is 
one  of  the  chief  factors  in  determining  the  distance  apart 
tJie  drains  should  be  placed  in  the  fielcl, 


Depth  of  Drains. 


295 


FIG.  114.— Tlie  upper  portion  is  a  diagram  of  flume  of  West  Los  Angeles 
Water  Company  and  vicinity.  Numbered  dots  show  where  level  ol 
ground  water  was  measured  in  wells  sunk  for  the  purpose,  and  cor- 
respond with  numbers  on  lower  part.  Lower  part,  profiles  of  the 
surface  of  the  ground  water  in  the  vicinity  of  the  West  Los  Angeles 
Water  Company.  The  heavily  shaded  line  is  the  ground  water  surface. 
Eacli  square  represents  100  by  10  feet. 


296       Ground  Water,  Wells  and  Farm  Drainage. 

367.  Distance   Between   Tile   Drains There   are   three 

prime  factors  which  determine  the  distance  between  tile 
drains.  1.  The  effective  size  of  soil  grains  and  pore  space 
of  the  subsoil  through  which  the  water  must  move  to  reach 
the  drain.  If  the  subsoil  has  a  close  fine  texture  the  re- 
sistance to  the  flow  will  be  great,  and  hence  the  water  sur- 
face will  rise  faster  back  from  the  drain,  bringing  it  near 
the  surface  .sooner  and  making  it  necessary  to  place  the 
lines  closer  together. 

2.  The  depth  at  which  the  drains  are  placed.    It  is  clear, 
that  when  it  is  desired  to  hold  the  water  midway  between 
a  line  of  tile  a  certain  distance  below  the  surface,  that  the 
deeper  the  tile  are  placed  the  further  they  may  be  apart, 
and  Fig.  115  illustrates  both  this  point  and  the  first. 

3.  The  interval  between  rainfalls  sufficiently  heavy  to 
produce  percolation.     In  regions  where  the  rainfall  is  both 
heavy  and  frequent  tiles  need  to  be  placed  nearer  together 
than  where  the  reverse  conditions  exist. 


FIG.  115.— Showing  the  influence  of  distance  between  tile  drains  on  the 
relation  of  the  ground  water  to  the  surface  of  the  ground. 

In  general  practice  for  field  crops  it  is  usually  sufficient 
to  place  the  lines  of  tile  from  50  to  100  feet  apart.  In 
favorable  cases  they  may  be  placed  even  further  apart  than 
this  and  in  special  cases  they  may  be  required  as  close  as 
30  feet. 


368.  Observed  Ground  Water  Surface  in  a  Tile  Drained 
Field. — In  Fig.  116  is  represented  the  observed  ground 


Depth  of  Drains. 


297 


water  surface  in  a  tile  drained  field  where  the  lines  are  33 
feet  apart,  3  to  4  feet  below  the  surface  and  where  the  sub- 
soil at  3  to  4  feet  and  below  is  sand.  The  slope  of  the  sur- 
face was  obtained  by  boring  wells  with  a  4-inch  auger  be- 
tween the  lines  of  tile  and  the  measurements  were  made  48 


FIG.   116. — Showing  the  observed  conformation   of   the  ground   water  sur- 
face in  a  tile  drained  field  48  hours  after  a   rainfall  of  .87  inch. 

hours  after  a  rainfall  of  .87  inch  May  13,  when  the  soil 
was  already  well  saturated.  On  this  date  the  highest  level 
above  the  top  of  3  inch  tile  between  any  two  lines  was  1 
foot  and  the  lowest  .3  foot. 

369.  Rate  of  Change  in  the  Contour  of  the  Ground  Water 
Surface  Between  Lines  of  Tile. — At  the  time  the  data  for  the 
last  section  were  taken  observations  were  also  made  to  de- 
termine the  rate  of  change  in  the  level  of  the  ground  water 
after  the  rain,  and  Fig.  117  represents  the  differences  in  the 
level  of  the  water  at  and  between  the  tile  drains  on  three 
different  dates.  It  will  be  seen  that  the  water  fell  fastest 
under  the  highest  ground  and  on  the  16th  was  below  the 
tile  in  the  upper  part  of  the  field. 


FIG.  117.— Showing  changes  In  the  level  of  the  ground  water  surface  ID 
a  tile  drained  field. 

This  illustration  makes  it  clear  also  how  the  tile  in  the 
lower  portion  of  the  field  make  their  influence  felt  in  the 


298       Ground  Water,  Wells  and  Farm  Drainage. 

upper  portion,  the  water  moving  as  indicated  by  the  long 
arrows. 

370.  Movement  of  Water  where  Heavy  Clay  Soils  are 
Underlaid  with  Sand. — When  a  heavy,  close  soil  is  underlaid 
with  sand  or  gravel  the  movement  of  water  toward  the  tile 
drains  will  be  almost  entirely  through  the  sand  when  the 
conditions  are  like  those  represented  in  Fig.  118.  In  such 
cases  the  rains  percolate  vertically  down  into  the  sand  and 
tlien  move  laterally  to  the  tile  drains,  where  it  rises  to  enter 
them,  as  shown  by  the  arrows. 


FIG.   118.— Showing  hew   the  main  flow   of  water  to  lines  of  tile   may  be 
through  a  subsoil  of  sand  when  this  is  present  and  near  the  surface. 

It  is  .clear  that  under  conditions  like  these  the  heavy  clay 
soil  above  does  not  determine  the  distance  apart  drains 
should  be  placed  but  rather  the  sand  stratum  below. 

371.  Fall  or  Gradient  for  Drains. — Generally  drains  should 
be  given  as  much  fall  as  the  conditions  will  permit  and  the 
gradient  should  not  be  less  than  2  inches  in  100  feet  if  this 
can  be  secured.      Cases  will  occur  where  less  must  be 
accepted  and  then  careful  leveling  must  be  done  to  secure 
the  largest  fall  available. 

It  will  often  happen  that  the  line  of  lowest  ground  is 
quite  tortuous,  making  the  distance  long,  and  on  this  ac- 
count making  the  fall  small.  Frequently  in  such  cases  cuts 
across  bends  can  be  made  by  digging  deeper,  in  this  way  in- 
creasing the  fall,  as  is  sometimes  done  in  straightening 
streams. 

372.  Uniform  Fall  Desirable — Effort  should  be  made  to 
secure  throughout  the  course  of  a  main  or  lateral  drain  a 
uniform  fall,  and  never,  where  it  can  well  be  avoided, 


Silt  Basin. 


299 


change  from  a  steeper  to  a  less  steep  grade,  because  if  this 
is  done  there  is  danger  that  sediment  may  lodge  where  the 
fall  is  less  and  close  up  the  drain.  The  case  is  different 
where  a  change  can  be  made  from  a  small  fall  to  one  which 
is  greater,  for  then  whatever  sediment  is  carried  by  the 
water  along  the  flatter  slope  will  be  carried  down  the  steeper 
one. 


TIG.  119.— Showing  the  construction  of  a  silt  basin. 

373.  Silt  Basin. — In  changing  from  a  steeper  gradient  to 
one  which  is  less  the  danger  of  clogging  the  tile  can  be  re- 
duced by  introducing  in  the  line,  at  the  place  where  the 
change  is  made,  a  silt  well,  Fig.  119,  which  provides  still 
water  in  which  sediment  falls  and  from  which  it  may  be  re- 
moved as  often  as  necessary.    Where  these  silt  basins  may 
be  small,  glazed  sewer  tile  of  suitable  size  may  be  used  for 
the  portion  above  the  ground. 

374.  Size  of  Tile — The  proper  size  of  tile  can  only  be  de~ 
finitely  stated  when  the  detailed  conditions  under  which  the 
drain  is  to  work  are  known.    They  should  be  large  enough 
to  remove  in  24  to  48  hours  the  excess  water  of  the  heaviest 
rains  likely  to  occur. 


300       Ground  Water,  Wells  and  Farm  Drainage. 

1.  Where  single  drains  are  laid  here  and  there  in  irreg- 
ular order  to  drain  low  places  larger  tile  are  required  than 
where  a  whole  area  is  systematically  treated,  because  in  the 
former  cases  a  larger  per  cent,  of  surface  water  from  sur- 
rounding higher  lands  will  flow  upon  the  low  areas  under 
which  the  drains  are  laid. 

2.  The  greater  the  fall  the  smaller  the  tile  may  be,— 
doubling  the  grade  increasing  the  carrying  capacity  nearly, 
one-third. 


FIG.  119a. — Apparatus  to  demonstrate  the  Influence  oi  head,  diameter, 
length,  and  bends  on  the  rate  of  discharge  of  water  through  lines  of 
tile  and  water  pipe..  •  . 

3.  The  areas  of  cross  section  of  tile  increase  with  the 
squares  of  their  diameters: 

If  their  diameters  are  in  the  ratio  of  2,  3,  4,  5,  6,  7,  their 
areas  will  be  in  the  ratio  of  4,  9,  16,  '25,  3G,  49,  but  as  the 


Size  of  Tile.  301 

friction  on  the  walls  of  small  tile  and  tlio  disturbance  due 
to  eddies  set  up  at  the  joints  are  greater  in  proportion  to  the 
amount  of  water  carried  the  capacities  of  tile,  running  full, 
increase  faster  than  the  squares  of  their  inside  diameters. 

4.  It  is  seldom  advisable  to  use  tile  smaller  than  3  inches 
in  diameter  because  so  little  variation  above  or  below  a  true 
grade  will  fill  them  with  sediment. 

5.  The  size  of  mains  must  vary  with  the  area  they  are  to 
drain,  with  their  fall  and  their  length.    C.  G.  Elliott  states 
that  where  drains  are  laid  3  feet  or  more  deep,  and  on  a 
grade  not  less  than  3  inches  in  100  feet,  a  2-inch  main  not 
more  than  500  feet  long  will  drain  2  acres. 

A  three  inch  tile  will  drain 5  acres. 

A  four  "        "      "       "     12     " 

A  five  "       "      "       "     20     " 

A  six  "       "      "       "     40     " 

A  seven     "       "      "       "     60     " 

He  specifies  further  that  a  2  inch  main  should  not  be 
laid  longer  than  500  feet  and  a  3  inch  not  longer  than  1,000 
feet. 

375.  A  Practical  Illustration  of  Sizes  and  Distances  Apart 
of  Drains. — The  sizes  of  mains  and  sub-mains,  the  sizes  of 
laterals,  the  lengths  of  each  size  used  and  the  distance  be- 
tween drains  may  be  most  clearly  and  briefly  stated  by 
citing  a  practical  example.  The  case  selected  is  an  80  acre 
field  laid  out  under  the  direction  of  C.  G.  Elliott  where  the 
soil  is  a  rich  black  loam  approaching  muck  in  its  lowest 
places  and  at  2.5  feet  underlaid  with  a  yellow  clay  subsoil. 
The  fall  of  the  main  is  not  less  than  2  inches  in  100  feet, 
the  laterals  being  more  rather  than  less.  This  area  is  repre- 
sented in  Fig.  120. 

The  main  begins  with  1,000  feet  of  7  inch  tile  carrying 
the  water  from  80  acres  of  flat  land  surrounded  by  level 
fields.  Next  follow  1,200  feet  of  6  inch,  then  600  feet  of  5 
inch  and  closing  with  157  feet  of  4  inch  tile  into  which  no 
laterals  lead.  Nothing  smaller  than  3  inch  tile  are  used  for 


#02       Ground  Water,  Wells  and  Farm  Drainage. 

laterals  and  the  least  distance  between  them  is  about  150 
feet. 


FIG.  120.— Drainage  system  of  80  acres.  Double  lines,  mains;  single  lines, 
laterals.  Numbers  give  length  and  diameter  of  tile.  (After  C.  G. 
Elliott. 

376.  Outlet  of  Drains. — Much  care  should  be  exercised  in 
selecting  the  location  for,  and  in  placing,  the  outlet.  It 
should  if  possible  have  a  free  outfall  as  shown  at  A,  Fig. 
121,  rather  than  to  end  beneath  water  as  at  B. 


FIG.  121.— A,  proper  outlet  for  drain;  B,  improper  outlet;  C,  proper  junc- 
tion of  lateral  witb  main;  D,  improper  junction. 


To  avoid  injury  from  freezing  in  cold  climates  the  last 
10  to  16  feet  of  the  main  should  end  in  glazed  sewer  tile  or 
in  the  glazed  drain  tile;  and  the  outlet  should  be  guarded 
with  masonry  and  covered  with  a  grating  to  keep  out  ani- 
mals. 


Connecting  Drains.  303 

377.  Connecting  Sub-main  with  Main — Where  a  sub-main 
joins  a  main  the  connection  should  be  made  at  an  acute 
angle  as  represented  at  C,  Fig.  121,  rather  than  at  right 
angles  as  at  D.      If  this  is  not  done  silt  will  collect  on  ac- 
count of  the  reduced  velocity  caused  by  the  meeting  of  the 
two  streams.       It  is  best  in  such  cases  to  use  the  manufac- 
tured junction  tile. 

378.  Joining  Laterals  with  Main. — The  junction  of  a 
lateral  should  if  possible  be  made  above  the  axis  of  the 
main,  cutting  a  hole  through  the  main  with  a  tile  pick; 
this  is  to  avoid  the  clogging  of  the  lateral.    Where  the  fall 
is  great  enough  to  admit  of  doing  so  one  of  the  best  unions 
with  a  main  Is  represented  in  Fig.  122,  the  end  of  the 
lateral  being  thoroughly  plugged  with  a  stone  bedded  in 
clay,  or  better  with  3  or  4  inches  of  cement. 


FIG.    122.— Method   of   connecting   lateral    with    main    drain.     (After   Jul. 

Kuhn.) 

Where,  on  account  of  small  fall,  the  lateral  must  ap- 
proach the  main  low  down  it  should  be  connected  in  the 
oblique  manner  represented  in  Fig.  121  at  C. 


379.  Obstructions  to  Drains — The  demand  for  water  by 
trees  is  so  great  that  they  must  not  be  permitted  to  grow 
within  3  or  4  rods  of  a  line  of  tile  which  has  water  running 
in  it  during  any  considerable  portion  of  the  growing  season. 
Fig.  123  represents  two  bunches  of  European  larch  roots 
taken  from  6  inch  tile  which  they  had  completely  closed. 
A  small  rootlet  entered  at  the  joint,  where  it  grew,  branched 


304       Ground  Water,  Wells  and  Farm  Drainage. 

and  expanded  until  its  fibrils  collected  so  much  silt  as  to 
completely  close  the  drain.  The  willow,  poplar,  elm,  larch 
and  soft  maple  are  among  the  trees  most  likely  to  make 
trouble  in  this  way. 


FIG.  123.— Roots  of  European  larch  removed  from  a  6-inch  tile  drain,  which 
they  had  effectually  clogged. 

380.  Laying  out  Drains. — Careful  study  should  be  given 
to  the  best  manner  of  laying  out  a  system  of  drains ;  the  aim 
being  to  secure  the  greatest  fall,  the  least  amount  of  dig- 
ging, the  least  outlay  for  tile  and  the  most  perfect  drainage. 
To  secure  these  results  drains  must  be  laid  so  that  no  two 
lines  are  taking  the  water  from  the  same  territory,  the  out- 
lets must  be  as  few  as  possible  and  only  as  large  tile  used 
as  are  needed  to  do  tlie  work. 


Laying  Out  Drains. 


305 


8'  3'  3' 


3*  3"  3 


3'  3'  3' 


FIG.  124.— Two  systems  for  laying  out  drains. 

In  Fig.  124  drains  are  laid  out  by  two  systems  for  the 
same  area  of  14  acres  with  the  lines  100  feet  apart.  By 
the  system  A  625  feet  of  4  inch  main  and  3,020  feet  of  3 
inch  laterals  are  required;  while  by  the  system  B  only  550 
feet  of  4  inch  and  2,830  feet  of  3  inch  tile  are  required  to 
cover  the  ground  so  as  to 
secure  equal  drainage.  It 
will  be  seen  that  in  the  sys- 
tem A  the  ends  of  all  the 
laterals  traverse  50  feet  of 
territory  drained  by  the 
main. 

When  long  lines  of  tile 
must  be  laid,  requiring 
more  than  one  size,  three 
systems  have  been  used: 
1st,  that  represented  at  A, 
Fig.  124;  2d,  that  at  A, 
125  and  3rd,  that  at  B,  125. 
In  the  second  case,  cover- 
ing an  area  2,000  feet  by 

900  feet,  above  the  line  a  a,        FIG.  125.-Two  systems  for  laying  out 

9,000  feet  of  4  inch  and  drains' 


306       Ground  Water,  Wells  and  Farm  Drainage. 


9,000  feet  of  3  inch  tile  are  laid  100  feet  apart ;  but  follow- 
ing the  third  system  only  3,000  feet  of  4  inch  and  15,300 
feet  of  3  inch  render  the  same  service  with  a  saving  of 
about  $33.00  for  tile. 

Usually  no  single  system  can  be  followed  but  the  slope 
and  shape  of  the  land  will  require  a  combination  of  two  or 
more. 

381.  Intercepting  Surface  Drainage In  very  many  cases 

where  drainage  is  required  the  necessity  is  caused  by 

the  collection  of  surface 
waters  from  the  surround- 
ing higher  lands.  It  may 
often  be  possible  in  such 
cases  to  avoid  a  large  part 
of  the  expense  of  under- 
drainage  by  intercepting 
and  controlling  the  sur- 
face waters,  collecting 
them  into  surface  drains 
and  leading  them  away  as 
represented  in  Fig.  120. 
In  this  case  the  water  is 

FIG.  128 -Method  of  intercepting  surface  Collected  illtO  a  SUrfaCC 
drainage.  A,  B,  surface  ditch.  (FromrUt/VU  Vva-Pnrp  it  rpnr>lnpQ  tlip 
Irrigation  and  Drainage.) 

low   area    and    is   carried 

around  on  the  higher  ground.  It  is  specially  important  to 
use  this  method  in  cases  where  low  areas  are  surrounded  on 
all  sides  by  a  rim  of  land  high  enough  to  prevent  the  con- 
struction of  underdrains. 

382.  Construction    of    Surface    Drains. — Where    surface 
waters  are  to  be  handled  as  in  (381)  it  can  usually  best  be 
done  by  constructing  broad   and   comparatively   shallow 
runways,  which  can  be  kept  in  permanent  grass,  the  widtli 
and  slope  of  the  ditch  being  such  that  a  wagon  and  mower 
can  readily  be  driven  along  and  across  it.  Such  waterways 
should  usually  be  1  to  2  feet  deep  and  10  to  15  feet  wide 


\ 


\ 


^Draining  Basins.  307, 

with  sides  sloping  gently,  to  a  flat  bottom  which  can  carry 
a  considerablevolume  of  water  slowly  without  being  eroded. 

383.  Intercepting  the  Underflow  from  Higher  Lands In 

a  very  large  number  of  cases  lands  require  drainage  be- 
cause of  the  underflow  of  water  from  the  adjacent  higher 
Jand  in  the  manner  indicated  in  Fig.  127.  In  such  cases, 


FIG.  127.— Showing  how  lines  of  tile  may  be  placed  at  A  and  B  to  inter 


cept  the  underflow  from  the  higher  land. 


when  drains  are  laid  along  the  foot  of  the  hill  below  the 
ground  water  surface,  as  represented  at  A  and  B,  much  of 
the  seepage  water  will  rise  into  the  drain  and  be  conveyed 
away  rather  than  flow  on  under  the  flat  land  beyond.  When 
such  corrections  as  these  are  made  it  may  even  be  unneces- 
sary to  underdrain  the  flat  land  or  when  the  drains  at  the 
foot  of  the  hill  do  not  fully  correct  the  evil  the  cost  is 
made  relatively  less. 

384.  Draining  Basins  Without  Outlets. — There  frequently 
occur  sinks  or  ponds  entirely  surrounded  by  rims  too  high 
to  permit  drainage  outlets  to  be  constructed  across  them. 
Such  cases  must  be  met  in  special  ways.  1.  Occasionally 
such  basins  are  underlaid  with  gravel  or  sand  which  is 
well  drained  and  the  water  is  retained  on  the  surface  only 
by  a  comparatively  thin  stratum  of  clay  subsoil.  When  tiiis 
is  true,  one  or  more  wells  may  be  sunk  through  the  clay 
into  the  sand  or  gravel,  as  represented  in  Fig.  128,  and 
filled  with  cobblestone  and  gravel.  Into  this  underdrains 
may  be  led  from  various  directions  to  collect  the  water 
and  bring  it  to  the  subterranean  outlet  thus  provided. 

2.  Where  several  acres  must  be  drained  the  above 
method  would  hardly  be  practicable  even  if  the  under- 
drainage  conditions  were  favorable.  It  is  possible,  how- 


308       Ground  Water,  Wells  and  Farm  Drainage. 

ever,  to  arrange  in  such  a  manner  that  a  good  windmill 
will  drain  a  considerable  bckly  of  land,  where  only  the 
underflow  must  be  dealt  .with  and  the  lift  is  less  than  20 
feet.  One  method  of  draining  by  wind  power  is  illustrated 
in  Fig.  129  where  A  is  one  of  a  number  of  closed  drains 


FIG.  128.— Method  of  draining  sinks. 


leading  to  a  collecting  basin,  D,  which  is  connected  with 
the  well  from  which  the  water  is  discharged  through  the 
pump  into  the  drain  C.  If  the  area  is  small  or  the  capacity 
of  the  pump  large  the  water  may  discharge  directly  into 
the  well,  which  may  be  provided  with  a  float  to  throw  the 


FIG.  129.— Method  of  draining  sinks  by  wind  power.     (From  Irrigation  and 

Drainage.) 

mill  out  of  gear  when  the  water  is  getting  too  low  for  the 
pump.  The  object  of  the  well  is  to  permit  the  mill  to  work 
during  the  winter. 

3.  In  still  other  cases  it  may  be  practicable  to  lay  the 
sink  off  into  lands  separated  by  broad,  open  "and  rather 
deep  ditches,  into  which  the  water  from  the  lands  could 
drain  and  where  evaporation  would  be  much  more  rapid 
than  from  the  soil.  To  increase  the  rate  of  evaporation  of 
water  from  the  ditches  lines  of  water  loving  trees,  like  the 
willow,  could  be  planted,  but  these  would  interfere  with 


Surface  Drainage. 


309 


cropping.    The  better  plan  would  be  to  utilize  the  ground 
with  a  crop  which  would  endure  the  shallow  drainage. 

385.  Lands  Requiring  Surface  Drainage. — There  are 
many  wide  stretches  of  very  flat  land  which  can  only  be 
drained  through  surface  channels.  Such  are  the  districts 
which  in  recent  geologic  times  were  lake  bottoms,  over 
which  a  heavy  sheet  of  close  textured  clay  was  deposited. 
Soils  like  these  have  subsoils  so  close  that  were  there  plenty 
of  fall  and  good  opportunity  to  find  outlets  for  drains  the 
rains  could  riot  reach  the  drains  freely  enough  to  meet  the 
needs  of  crops. 


FIG.  130.— Plan  for  drainage  of  lands  of  the  Illinois  Agricultural  Company, 
Rontoul,  Illinois.  (After  J.  O.  Baker.)  The  smallest  squares  are  40 
acres;  double  lines  show  open  ditches;  single  lines  are  tile  drains. 

Such  fields  must  be  plowed  in  narrow  lands  with  the 
dead  furrows  in  the  direction  of  greatest  fall  in  order  to 
provide  a  quick  removal  of  the  surplus  rains. 

Other  districts  are  so  flat  that  the  rains  have  not  yet 
been  able  to  cut  sufficiently  deep  river  channels  to  dram 
the  fields  enough  for  agricultural  purposes.  The  soil  may 
be  porous  enough,  even  a  coarse  sand,  and  yet  for  lack  of 
natural  drainage  channels  remain  too  wet  to  till. 


310      Ground  Water,  Wells  and  Farm  Drainage. 

In  such  cases  deep  open  ditches  must  be  provided  to  con- 
vey the  water  out  of  the  country,  serving  as  outlets  for 
underdrains  laid  in  the  adjoining  fields.  A  district  of  this 
type  of  land  drainage  is  represented  in  Fig.  130,  covering 
nearly  six  square  miles.  The  double  lines  represent  deep 
open  ditches  and  the  single  lines  underdrains. 

Another  drainage  system  of  .this  sort  in  Mason  and 
Tazvvell  counties,  111.,  has  17.5  miles  of  main  ditch  30  to 
60  feet  wide  at  the  top  and  8  to  11  feet  deep.  Leading 
into  these  mains  there  are  five  laterals  30  feet  wide  and  Y 
to  9  feet  deep,  the  whole  system  embracing  TO  miles  of 
open  ditch  for  the  purpose  of  providing  outlets  for  under- 
drains. 


CHAPTER    XV. 
PRACTICE  OF  ITNDEEDRAINAGE. 

The  best  work  in  underdraining  can  only  be  done  by  tlie 
man  who  has  a  thorough  grasp  of  the  principles  of  the  art 
and  who  has  had  enough  practical  experience  to  make  him 
perfectly  familiar  with  the  essential  details  as  they  vary 
with  soil,  topography,  climate  and  crop  conditions. 

There  are  many  cases  of  local  drainage  where  the  area 
and  expense  involved  are  small,  where  the  farmer  having 
a  fair  knowledge  of  the  principles  of  drainage  can  super- 
vise or  do  his  own  work,  but  when  large  areas  are  to  be 
underdrained,  where  the  fall  is  small  and  the  surface  con- 
ditions complex,  it  will  be  safest  'to  entrust  the  leveling 
and  staking  out  of  the  mains  and  laterals  ready  for  the 
ditcher  to  a  competent  and  thoroughly  reliable  drainage 
engineer. 

Indeed  it  will  generally  be  best  and  more  economical  to 
let  the  whole  job  if  it  is  large  and  difficult  to  a  man  of  ex- 
perience who  has  established  a  reputation  for  reliable  work. 
Even  in  the  matter  of  digging  the  ditch,  raid  particularly 
in  giving  it  its  finish,  as  well  as  in  placing  the  tile,  drainage 
engineers  find  it  difficult  to  find  men  who  have  the  pa- 
tience, the  feeling  of  responsibility  and  the  practical  skill 
to  do  it  well.  A  man  who  has  the  right  frame  of  mind  and 
the  skill  to  do  this  finishing  and  most  important  work  we1.! 
is  much  more  to  be  trusted  than  the  farmer  himself  who 
has  so  many  duties  to  distract  his  attention  and  tempt  him 
to  rush  the  job. 

But  while  the  general  farmer  should  not  be  encouraged 
to  attempt  the  draining  of  large  and  difficult  areas  on  his 


312       Ground  Water,  Wells  and  Farm  Drainage. 

own  place  it  is  quite  important  for  him.  to  have  a  clear  con- 
ception of  the  general  principles  of  drainage  and  of  what 
constitutes  thoroughly  good  detail  practice. 


FIG.  131.— Showing  forms  of  drainage  tools. 

38G.  Means  for  Determining  levels.  — As  a  general  rule 
the  laying  out  of  a  system  of  drains  should  only  be  at- 
tempted with  good  instruments,  two  of  which  are  repre- 
sented in  Fig.  131.  Where  a  good  drainage  level  cannot  be 
had  the  best  substitute  is  the  water  level,  one  form  of 
which  is  represented  in  Fig.  131  and  another  in  Fig.  132 ; 
which  consists  of  a  piece  of  gas  pipe  about  3  feet  long 
mounted  on  a  standard  and  provided  with  two  elbows  into 
which  are  cemented  two  pieces  of  water  gauge  glass.  When 
the  instrument  is  filled  with  water  the  surfaces  in  the  two 
tubes  stand  on  a  level  and  can  be  used  to  sight  across.  To 
move  the  instrument  close  the  ends  of  the  tubes  with  corks. 

As  a  substitute  for  the  gas  pipe  a  piece  of  rubber  tubing 
may  be  used  or  a  piece  of  garden  hose. 

A  less  reliable  level  can  be  improvised  by  arranging  an 
arm  upon  a  standard  upon  which  a  carpenter's  level  may 
be  set.  Or  a  still  more  crude  level  may  be  made  from  a 


Means  for  Leveling. 


carpenter's  square  mounted  on  a  horizontal  arm  on  which 

a  plumb  bob  is  suspended, 

with    which     to    set    the 

square  with  its  long  arm 

level. 


387.  Leveling  a  Field. — . 
In  determining  the  differ- 
ences of  level,  in  different 
parts  of  a  field  it  is  desired 
to  drain,  the  simplest 
method  for  the  inexper- 
ienced person  is  to  lay  out 
the  field  into  squares  of 
100  or  more  feet,  driving 
short  stakes  at  the  corners. 

Set  the  instrument  at  a, 
Fig.  133,  midway  between  V 

the   stations    1-1    and    1-? 

j  i    ,1  T  ,H'  IG.  132. -Showing  cue  form  of  water  level. 

and  record  the  reading  oi 
the  target  placed  upon  the 

stake  at  1-1  in  the  table  in  the  column  headed  "back-sight" 
which  is  assumed  for  illustration  to  be  4  feet.  Next  turn 
the  instrument  upon  stake  1-2,  when  its  distance  below  the 
level  is  found  to  be  3.8  feet  and  is  entered  in  the  column 
headed  "fore-sight."  This  shows  that  the  ground  at  1-2  is 

4ft.  —3.8ft.  =.2  ft. 

higher  than  station  1-1. 

In  the  column  headed  "Elevation"  the  first  station  is 
given  arbitrarily  a  hight  of  10  feet  above  an  assumed 
da'tum  plane  to  avoid  minus  signs.  The  level  is  now  trans- 
ferred to  b  and  the  distance  of  1-2  below  the  instrument 
found  to  be  4.2  feet  which  is  entered  in  the  column  "back- 
sight" as  before.  Turning  now  upon  1-3,  its  reading  is 
found  to  be  4  feet  and  this  is  entered  in  th*1  column  "fore- 
sight." 

The  difference  in  level  between  the  back  sight  and  fore 
sight  shows  the  difference  in  level  between  the  two  stations 


314      Ground  Water,  Wells  and  Farm  Drainage. 

and  is  placed  in  the  column  headed  "difference."  The  first 
difference  added  to  the  datum,  10,  gives  10.2,  the  hight 
of  station  1-2  above  the  datum  plane.     The  second  differ- 
VI  V  IV  III  II  I 


FIG.  133.— Showiijg  method  of  leveling  a  field. 

ence,  .2,  added  to  the  elevation  of  station  1-2  gives  10.4, 
the  elevation  of  station  1-3  above  datum.  In  this  manner 
the  level  is  moved  from  station  to  station  until  e  is  reached 
when  it  is  transferred  to  f  and  back  sights  r.nd  fore  sights 
taken  as  before,  and  entered  in  the  table  to  connect  the 
first  line  of  observations  with  the  new  one  jr.st  begun. 

Proceeding  as  before  the  level  is  moved  from,  f  to  g  and 
then  through  h,  i,  j,  k  and  1  to  m  and  so  on  until  the  field 
is  all  completed.  When  proceeding  from  higher  to  lower 
levels  the  differences  must  be  subtracted  rather  than  added 
to  obtain  the  elevation  of  the  lower  station.  Fig.  104  shows 
the  relation  of  the  level  to  the  target  'rod  along  a  single 
line  of  stations  shown  in  profile. 


Location  of  Drains. 


315 


Table  giving  data  obtained  in  leveling  field  of  Pig.  133. 


Station. 

Back-sight. 

Fore-sight. 

Difference. 

Elevation 

1-1 

4 

10 

1-2 

4.2 

3.8 

.2 

10.2 

1-3 

3.8 

4 

.2 

10.4 

1-4 

4 

3.6 

.2 

10.6 

1-5 

3.9 

38 

.2 

10.8 

1-6 

4 

3.7 

.2 

11 

II-6 

38 

3.98 

.02 

11.02 

11-5 

3.9 

3.995 

.195 

10.825 

II-4 

4 

4.095 

.195 

10  63 

II-3 

4.1 

4.19 

.19 

10.44 

11-2 

3.9 

4.26 

.16 

10.28 

II-l 

3.8 

3.98 

.08 

10.2 

1II-1 

4 

3.6 

_o 

10.4 

III-3 

3.9 

3.96 

.'04 

10.44 

III-3 

4.2 

3.775 

.125 

10  5G5 

III  4 

4.1 

4.045 

.155 

10.72 

1II-5 

3.8 

3  93 

.17 

10.  "9 

111-6 

4.1 

3.625 

.185 

11.075 

IV-6 

4 

4.185 

.085 

11.16 

1V-5 

3.84 

.16 

11 

388.  Contour  Map  of  Field. — When  the  field  has  been  laid 
out  as  represented  in  Fig.  133,  and  the  elevations  of  the 
several  stations  transferred  to  the  map,  the  figures  show  at 


- . 


FIG.  134.— Showing  method  of  leveling. 

a  glance  where  the  field  k  high  and  where  it  is  low.  If 
now  lines  are  drawn  upon  the  map  through  all  places  hav- 
ing the  same  elevation  the  topography  of  the  field  becomes 
still  more  evident  to  the  eye.  Such  lines  are  called  con- 
tours or  contour  lines,  and  such  are  the  dotted  lines  in  the 
map. 

389.  location  of  Mains  and  laterals. — It  is  clear  from  the 
contour  map  that  the  highest  station  in  the  field  is  VI — 6 
and  the  lowest  1-1.  If  then  we  are  seeking  the  steepest  fall 
or  gradient  for  the  main  it  will  be  found  along  a  straight 


316       Ground  Water,  Wells  and  Farm  Drainage. 

line  connecting  these  two  stations.  Of  course  no  field  will 
be  found  with  so  regular  a  slope  as  this  but  the  principle 
is  no  less  true  for  being  so  simply  stated. 

vi       v       rv       m       n        i 


^10.  135.— Showing  a  system  of  tile  drains  laid  out  on  the  leveled  field  of 
Fig.  133.    (From  Irrigation  and  Drainage.) 

If  such  a  field  is  to  be  drained  by  placing  laterals  100 
feet  apart  about  the  maximum  fall  for  them,  and  the  mini- 
mum amount  of  tile  and  ditching,  will  be  secured  by 
placing  the  laterals  along  the  lines  of  leveling,  in  which 
case  the  lines  I,  II,  III,  IV,  V,  VI  will  constitute  the 
laterals  on  one  side  of  the  main  and  the  lines  1,  2,  3,  4,  5,  6 
the  laterals  on  the  other  side,  as  represented  in  Fig.  135, 
Since  the  lines  I  and  1  are  both  radii  of  the  same  circle  and 
have  the  same  elevation  at  their  outer  extremities  the  fall 
or  gradient  will  be  the  same  or  .2  of  a  foot  per  100  feet,  as 
shown  on  the  contour  map,  but  along  the  lines  Y  and  5  the 
gradient  will  be  .15  feet  per  100  feet  or  1.8  inches  instead 
of  2.4  inches  per  100  feet  along  the  lines  I  and  1.  The  fall 


Location  of  Drains. 


317 


is  therefore  not  uniform  for  all  the  laterals  nor  can  it  be 
when  they  are  placed  along  parallel  lines. 

If  the  field  required  drains  every  50  feet  then  a  greater 
mean  fall  could  be  secured  and  less  tile  would  be  required 
if  a  system  like  that  of  Fig.  136  were  adopted. 


FIG.    136.— Showing   a    second    system   ot   drains   laid    out   on   the   field  of 
Fig.  133.    (From  Irrigation  and  Drainage.) 

390.  Laying  Out  Drains — When  the  positions  of  the 
mains  and  laterals  have  been  decided  the  next  step  is  to 
mark  them  with  "grade  pegs"  and  "finders."     The  grade 
pegs  are  short,  driven  securely  into  the  ground  just  to  one 
side  of  the  intended  ditch,  and  are  placed  at  regular  inter- 
vals apart.     To  one  side  of  the  grade  pegs  are  placed  longer 
ones  called  "finders"  upon  which  is  to  be  recorded  the 
depth  below  the  grade  peg  the  ditch  is  to  be  dug. 

391.  Determining  the  Grade  and  Depth  of  the  Ditch. In 

doing  this  work  the  leveling  begins  at  the  outlet  and  the 


318       Ground  Water,  Wells  and  Farm  Drainage. 


steps  are  the  same  as  those  already  described  for  the  field 
leveling,  the  results  being  recorded  in  a  table  calling  for 
two  more  columns  when  worked  out  than  were  needed  in 
the  field  work.  These  are  indicated  in  the  table  below : 

Table  showing  Field  Notes  for  determining  depth  of  ditch  and 
grade  of  drain. 


Station 

Back-sight 

Fore-sight. 

Difference. 

Elevations 

Grade  -line 

Depth  of 
ditch. 

Outlet 

7 





7 

7 

0 

0 

4 



3 

10 

7 

3 

50 

3.97 

3.87 

.13 

10.13 

7.12 

3.01 

100 

4.2 

3.83 

.14 

10.27 

7.24 

3.03 

150 

4.1 

4.08 

.12 

10.39 

7.36 

3,03 

200 

3.95 

3.99 

.11 

10.5 

7.48 

3.02 

250 

3.87 

3.82 

.13 

10.63 

7.6 

3.02 

300 

4 

3.69 

.18 

10.81 

7.72 

3.09 

350 

4.25 

3.83 

.17 

10.98 

7.84 

3.14 

400 

4.08 

4.1 

.15 

11.13 

7.96 

3.17 

450 

4.05 

3.96 

.12 

11.25 

8.08 

3.17 

500 

3.97 

395 

.1 

11.35 

8.2. 

3.15 

550 

3.75 

3.97 

__ 

11.35 

841 

3.03 

600                

3.74 

0.1 

11.36 

8.14 

2.93 

In  "Fig.  13T,  which  is  a  profile  of  the  data  in  the  table 
showing  the  outlet  of  the  drain  at  A,  the  first  stake  at  O 
and  the  second  at  50,  etc.,  up  to  600,  both  the  lines  of 
grade  and  the  datum  plane  are  shown.  On  each  numbered 
stake  is  given  the  depth  of  the  ditch  below  the  top  of  the 
grade  peg,  and  below  the  peg  has  been  set  the  hight  of  the 
bottom  of  the  ditch  above  the  datum  plane. 

Since  the  outlet  in  this  case  is  7  feet  above  datum  and 
the  s'urface  at  600  feet  is  11.36  feet  the  total  fall  is 
11.36  feet  — 7  feet  =  4.36. 

But  if  the  depth  of  the  ditch  at  the  upper  end  is  made 
2.92  feet  the  available  fall  will  then  be 

4.36  feet  —  2.92  feet  =  1.44. 
Since  the  ditch  is  12  times  50  feet  long  the  fall  will  be 

~~  =  .12  feet  per  50  feet. 

or  .24  feet  per  100  feet.    At  each  50  foot  station  then  the 
bottom  of  the  ditch  above  datum  plane  will  be  found  by 


Determining  Grade. 


119 


adding  .12  foot,  to  7  feet,  which  is  the  height  of  the  outlet, 
for  that  of  the  second  station;  then  .12  feet  added  to  this 
gives  the  third  station  and  so  on,  thus: 

7,  7.12,  7.24,  7.36,  7.48,  7.60,  7.72,  7.84,  7.96,  8.08, 
8.20,  8.32,  8.44. 


o      so     IN   "?     r 


800   850   SOO   «>   *?0   450   500   550   600 


FiQ.  137.— Profile  of  ditch  staked  ready  for  digging,  with  depths  for  the 
ditch  at  the  several  stations. 

If  these  numbers  are  subtracted  from  the  hights  of  the 
surface  of  the  ground  at  the  respective  places  the  differ- 
ence will  be  the  depth  the  ditch  must  be  dug  at  those 
places,  and  the  figures  which  are  placed  upon  the  finders 
for  the  instruction  of  the  men  in  digging.  These  figures 
are.  given  in  the  table  in  the  column  "depth  of  ditch." 

The  experienced  drainage  engineer  with  accurate  tele- 
scope level  makes  the  details  of  leveling,  establishing  the 
gra'de  and  marking  the  grade  pegs  simpler  than  here  given 
but  it  is  not  safe  for  a  fanner  with  a  cheap  level  to  follow 
his  methods. 

392.  Changing  from  One  Grade  to  Another It  may  hap- 
pen in  laying  out  the  ditch  that  it  is  impracticable  to  fol- 
low a  single  grade  on  account  of  having  to  dig  too  deep  in 
some  places  or  of  leaving  the  tile  too  close  to  the  surface 
in  others.  Suppose  in  the  last  profile  (391)  the  ditch  was  to 
be  500' feet  longer  and  that  in  this  500  feet  there  had  been 


320       Ground  Water,  Wells  and  Farm  Drainage. 


Digging  Ditches. 


321 


a  rise  of  but  6  inches.  It  is  clear  that  to  hold  a  single  grade, 
making  the  upper  end  of  the  ditch  2.92  feet  deep,  would 
require  a  greater  depth  in  other  portions  than  necessary. 
But  if  the  grade  is  changed  at  the  600  foot  station  so  as 
to  give  a  fall  of 

•5-ft"    =  .1  ft.  per  100  ft. 
o 

a  sufficient  depth  will  be  secured  and  labor  in  digging 
saved. 


FIG.  f3y. — Showing  the  ditching  line  and  the  commencement  of  digging. 

393.  Ditching  Tools — In  digging  a  ditch  it  is  a  matter  of 
first  importance  to  have  suitable  tools ;  and  whatever  else  is 


322       Ground  Water,  Wells  and  Farm  Drainage. 

chosen  the  men  should  be  provided  with  first  class  spades, 
kept  sharp  and  free  from  rust.  The  spade  which  gives  the 
best  satisfaction  has  a  long,  thin,  narrow  and  curved  blade. 
The  curvature  is  of  first  importance  in  giving  greater  stiff- 
ness and  allowing  the  blade  to  be  made  thinner  and  lighter. 
The  spade  should  be  narrow  and  thin  to  enable  the  user  to 
force  it  full  length  into  the  soil  with  the  pressure  of  the 
foot  and  so  as  to  be  able  to  leave  the  bottom  of  the  ditch 
narrow,  removing  as  little  earth  as  possible. 

In  Fig.  131  are  shown  two  forms  of  spades,  four  tile 
hoes,  which  are  used  in  finishing  the  bottom  of  the  ditch 
and  removing  the  loose  earth,  and  a  tile  hook,  used  in  plac- 
ing the  tile.  The  series  of  half  tones  shows  these  different 
tools  in  use. 

394.  Making  the  Ditch  Narrow  and  Straight. — To  make 
the  ditch  straight  a  strong  light  line  is  stretched  taut  near 
the  surface  and  4  inches  back  from  the  edge.     If  the  ditcb 
is  to  be  only  2.5  to  3  feet  deep  it  need  be  no  wider  at  the 
top  than  one  foot,  as  shown  by  the  length  of  tile  in  Fig. 
139.     Where  the  ditch  must  be  4.5  to  5  feet  and  receive  a 
6  inch  tile,  as  shown  in  Fig.  141,  it  must  have  a  width  at 
the  top  of  15  to  18  inches. 

The  ditcher  is  trained  to  cut  the  walls  straight  with  an 
even  slope  to  the  bottom  so  as  to  leave  a  straight  line 
along  the  bottom  to  receive  the  tile.  In  Fig.  140  it  will  be 
seen  that  four  men  are  working  in  line  to  complete  the 
depth  of  the  ditch  which  is  4.5  feet  at  the  place. 

395.  Shaping  the  Bottom  and  Bringing  It  to  Grade. — In 
Fig.  141  the  man  in  the  foreground  is  using  the  tile  hoe  to 
clean  out  the  last  loose  earth  and  to  bring  the  bottom  to 
grade  and  proper  shape  to  receive  the  tile.     The  grade  is 
secured  by  stretching  the  ditcher's  line  tight,  and  on  the 
slant  the  bottom  of  the  ditch  is  to  be  given,  and  at  a  known 
hight  above  it.     It  is  then  only  necessary  for  the  exper- 
ienced man  to  use  a  measuring  rod  to  secure  the  depth  and 
grade  desired. 


Digging  Ditches. 


323 


324       Ground  Water,  Wells  and  Farm  Drainage. 

When  the  requisite  skill  and  judgment  have  not  been 
acquired  for  this  work  the  man  is  provided  with  a  meas- 
uring stick  with  a  sliding  arm  which  extends  at  right 
angles  to  the  rod  and  long  enough  to  reach  the  grade  line. 
It  is  then  only  necessary  to  hold  the  rod  or  "ditcher's 
square"  plumb  to  know  whether  the  ditch  has  the  depth 
desired. 

396.  Placing  the  Tile. — When  the  ditch  has  been  finished 
the  tile  are  laid  with  the  tile  hook,  as  represented  in  Fig. 
142.  With  the  aid  of  this  tool  they  are  placed  rapidly 
and  accurately  without  getting  into  the  ditch.  Great  care 
should  always  be  taken  to  turn  and  shift  the  tile  until  a 
perfectly  close  joint  is  made  all  around.  It  does  not  do  to 
simply  have  them  meet  on  the  upper  edge,  they  should  fit 
squarely  and  closely  through  the  entire  circumference  and 
if  necessary  tile  too  much  warped  to  permit  of  this  must 
be  discarded. 

Some  prefer  to  place  the  tile  with  the  hand,  standing  in 
the  ditch  upon  them,  covering  them  as  rapidly  as  laid  with 
4  to  6  inches  of  earth,  taking  care  to  get  it  thoroughly 
packed  and  not  to  get  the  tile  out  of  alignment. 

The  greatest  care  should  be  exercised  to  pack  the  earth 
thoroughly  about  the  joints  so  as  to  avoid  large  open 
cavities  through  which  the  water  may  rush  during  heavy 
rains,  washing  dirt  into  the  tile. 

Tile  laying  should  begin  at  the  outlet  of  the  mainr  pro- 
ceeding upward  to  the  first  lateral,  where  the  junction 
should  be  made  and  tile  enough  laid  in  the  lateral  to  per- 
mit the  main  to  be  partly  filled.  The  main  may  then  be 
carried  on  until  the  next  lateral  is  reached,  when  this 
should  be  commenced  as  before.  Care  should  be  exercised 
not  to  leave  the  upper  end  of  an  unfinished  line  of  tile  open 
for  heavy  rains  to  wash  mud  into  it.  If  the  line  cannot  be 
finished  before  the  rain  the  end  may  be  guarded  by  closing 
it  with  a  board,  brick  or  bunch  of  grass. 


Digging  Ditches. 


325 


21 


326       Ground  Water,  Wells  and  Farm  Drainage. 


Digging  Ditches. 


327 


328       Ground  Water,  Wells  and  Farm  Drainage. 

397.  Filling  the  Ditch — After  the  tile  have  heen  placed 
and  covered  with  the  first  layer  of  earth  the  balance  may 
be  put  in  by  any  convenient  method.  A  common  and  ex- 
peditious way  is  represented  in  Fig.  143  where  a  plow  is 
drawn  by  a  team  attached  to  a  long  evener.  For  the  finish- 
ing the  ordinary  road  grader  makes  an  efficient  tool. 

Still  another  method  is  to  use  a  light  board  scraper  pro- 
vided with  handles  to  be  held  against  the  bank  of  earth, 
which  is  drawn  into  the  ditch  by  a  team  on  the  opposite 
side  drawing  from  a  rope  and  backing  when  the  scraper  is 
emptied. 


PRINCIPLES  OF  RURAL  ARCHITECTURE, 


CHAPTER  XVI. 
STRENGTH  OF  MATERIALS. 

A  knowledge  of  the  principles  governing  the  strength  of 
materials  is  helpful  along  many  lines  of  farm  practice  and 
particularly  in  the  construction  of  farm  buildings. 

398.  A  Stress. — When  a  post  is  placed  upon  a  foundation 
and  a  load  of  two  thousand  pounds  set  upon  it  the  post  is 
undergoing  or  opposing  a  stress  of  two  thousand  pounds. 
When  a  rope  is  supporting  a  load  of  one  thousand  pounds 
in  a  condition  of  rest  it  is  subject  to  a  stress  of  one  thou- 
sand pounds.  The  joists  under  a  mow  of  hay  are  subjected 
to  a  stress  measured  by  the  tons  of  hay  which  they  carry. 

399.  Kinds  of  Stress — Solid  bodies  may  be  subjected  to 
three  kinds  of  stress  which  tend  to  break  them  and  will 
do  so  if  the  stress  is  great  enough.    These  are : 

1.  A  crushing  stress,  where  the  load  tends  to  crowd  the 
molecules  closer  together,   as  when  kernels  of  corn  are 
crushed  between  the  teeth  of  an  animal. 

2.  A  stretching  stress,  as  where  a  cord  is  broken  by  a 
load  hung  upon  it. 

3.  A  twisting  stress,  as  where  a  screw  is  broken  by 
trying  to  force  it  into  hard  wood  with  a  screw-driver. 

400.  Strength  of  Moderately  Seasoned  White  and  Yellow 
Pine  Pillars. — Mr.  Chas.  Shaler  Smith  has  deduced,  from 
experiments  conducted  by  himself,  the  following  rule  for 


330 


Rural  Architecture. 


strength  of  moderately  seasoned  white  and  yellow  pine 
pillars: 

Rule. — Divide  the  square  of  the  length  in  inches  by  the 
square  of  the  least  thickness  in  inches;  multiply  the  quo- 
tient by  .00  4  and  to  this  product  add  1;  then  divide  5,000 
by  this  sum  and  the  result  is  the  strength  in  pounds  per 
square  inch  of  area  of  the  end  of  the  post.  Multiply  this 
result  by  the  area  of  the  end  of  the  post  in  inches,  and  the 
answer  is  the  strength  of  the  post  in  pounds. 

In  applying  this  rule  in  the  construction  of  farm  build- 
ings the  timbers  should  not  be  trusted  with  more  than  one- 
fourth  to  one-sixth  of  the  theoretical  load  they  are  com- 
puted to  carry,  because  the  theoretical  results  are  based 
upon  averages,  and  there  is  a  wide  variation  in  the  strength 
of  individual  pieces. 

Table  of  breaking  load  in  tons,  of  rectangular  pillars  of  half 
seasoned  white  or  yellow  pine  firmly  fixed  and  equally 
loaded,  computed  from  C.  S.  Smith's  formula. 


•si 

g-8 
AS 

Dimensions  of  rectangular  pine  pillars  in  inches. 

4x4 

4x6 

4x8 

4x10 

4x12 

6x6 

6x8 

6x10 

6x12 

8x8 

8x10 

8x12 

10x10 

10x12 

8. 
10.    . 
12.     . 
14.     . 

16.  . 

18... 

tons 
12  1 

8.7 
65 
5.0 
3.9 

tons 
18.1 
13.0 
9.7 
7.4 
5.9 

tons 
24.2 
17.4 
12.9 
9.9 
7.8 

tons 
30.2 
21.7 
16.1 
12.4 
9.8 

tons 
36.3 
26.1 
19.4 
14.9 
11.7 

tons 
44.5 
31.6 
27.2 
21.7 
17.7 
14.6 
12  2 
10.3 
8.8 

tons 
59.3 
46.2 
S6.3 
29.0 
23.5 
19.4 
16.2 
13.7 
11.7 

tons 
74.1 
57.7 
45.4 
36.2 
29.4 
24.3 
20.  3 
17.2 
14.7 

tons 
88.9 
69  2 
54  4 
43.5 
35.3 
29.1 
24.3 
20.6 
17.6 

tons 
101.7 
84.2 
69.7 
57.9 
48.4 
40.8 
34.8 
29.9 
25.9 

tons 
126.9 
105.3 
87.1 
72  3 
60.6 
51.0 
43.4 
37.4 
32.3 

tons 
152.3 
126.3 
104.5 
86.8 
72.7 
61.2 
52.1 
44.8 
38.8 

tons 
182.7 
158.6 
136.7 
117.4 
101.0 
87.2 
75.7 
65.8 
57.9 

tons 
219.2 
190.3 
164.0 
140.9 
121.2 
102.6 
90.8 
79.0 
69.4 

20 

22. 

24.... 

In  the  application  of  the  rule  for  the  crushing  load  for 
posts  in  barn  building  the  length  referred  to  is  the  greatest 
distance  between  any  supports  which  prevent  the  post  from 
bending. 

401.  Bearings  for  Posts. — In  order  that  a  post  may  carry 
its  maximum  load  it  is  important  that  it  rests  squarely 
upon  its  support  and  that  the  load  carried  presses  squarely 
upon  the  post.  If  the  ends  of  the  post  are  not  square  or  if 


Strength  of  Materials. 


331 


the  bearing  is  out  of  true  so  that  the  strain  comes  upon  one 
edge  the  carrying  power  is  greatly  lessened. 

402.  Tensile  or  Stretching'strength  of  Timber. — The  ten- 
sile strength  of  materials  is  measured  by  the  least  weight 
which  will  break  a  vertical  rod  one  inch  square  firmly  and 
squarely  fixed  at  its  upper  end,  the  load  hanging  from  the 
lower  end.  Below  are  given  the  results  of  experiments 
with  different  varieties  of  wood,  but  the  strengths  vary 
greatly  with  the  age  of  the  trees,  with  the  part  of  the  tree 
from  which  the  piece  comes,  the  degree  of  seasoning,  etc. 


Elm 6,000  Ibs 

American  hickory 11, 000  Ibs 

Maple 10, 000  Ibs 

Oak,  white  aud  rod 10, 000  Ibs 

Poplar 7, 000  Ibs 

White  pine 10,000  Ibs 


per  square  inch, 
per  square  inch, 
per  square  inch, 
per  square  inch, 
per  square  inch, 
per  square  inch. 


403.  Tensile  or  Cohesive  Strength  of  Other  Materials.— 


American  cast  iron 16, 000  to  28,000  Ibs.  per  sq. 

Wrought  iron  wire,  annealed 30,000  to  60,000  Ibs.  per  sq. 

Wrought  iron  wire,  hard 50,000  to  100, 000  Ibs.  per  sq. 

Wrought  iron  wire  ropes,  per  sq.  in.  of  ropo 38,000  Ibs.  per  sq. 

Leather  belts,  1,500  to  5,0'JO,  good 3,000  Ibs.  per  sq. 

Rope,  manila,  best 12, COO  Ibs.  per  sq. 

Rope,  hemp,  bott 15,000  Ibs.  per  sq. 


neb. 
nch. 
nch. 
nch. 
nch. 
nch. 
nch. 


404.  Transverse  Strength  of  Materials. — When  a  board  is 
placed  upon  edge  and  fixed  at  one  end  as  represented  at  A, 
Fig.  144,  a  load  acting  at  W  puts  the  upper  edge  under  a 
stretching  stress. 


We  know  from  experience  that  in  case  the  board  breaks 
under  its  load  when  so  situated  the  fracture  will  occur 


332  'Rural  Architecture. 

somewhere  near  5-6.  Now  in  order  that  this  may  take 
place  there  must  be,  with  white  pine,  according  to  (402)  a 
tensile  stress  at  the  upper  edge  of  ten  thousand  pounds  to 
the  square  inch,  and  if  the  board  is  one  inch  thick  the  upper 
inch  should  resist  a  stress  of  10,000  pounds  at  any  point 
from  5  to  1;  but  we  know  that  no  such  load  will  be  carried 
at  W.  The  reason  for  this,  and  also  for  its  breaking  at  5 
rather  than  at  any  other  point,  is  found  in  the  fact  that  the 
load  acts  upon  a  lever  arm  whose  length  is  the  distance 
from  the  point  of  attachment  of  the  load  to  the  breaking 
point,  wherever  that  may  be,  and  this  being  true  the  great- 
est stress  comes  necessarily  at  5. 

If  the  board  in  question  is  48  inches  long  and  6  inches 
wide,  it  will,  in  breaking,  tend  to  revolve  about  the  center 
of  the  line,  5-6,  and  the  upper  three  inches  will  be  put 
under  the  longitudinal  strain  but,  according  to  (402),  ia 
capable  of  withstanding 

3  X  10,000  Ibs.  =  30,000  Ibs. 

without  breaking;  but  in  carrying  the  load  at  the  end  as 
shown,  this  cohesive  power  is  acting  at  the  short  end  of  a 
bent  lever  whose  mean  length  of  power  arm  is  one-half  of 
4-5  or  1.5  inches,  while  the  weight  arm  is  forty-eight 
inches  in  length.  It  should  therefore  only  be  able  to  hold 
at  W  937.5  pounds,  for 


we  have  30,  000  X  1.5  =  W  X  48. 
whence  W  =  ^^  =  937.5  Ibs. 

When  a  board,  in  every  respect  like  the  one  in  A,  Fig. 
144,  is  placed  under  the  conditions  represented  in  either  B 
or  C,  Fig.  144,  it  should  require  just  four  times  the  load  to 
break  it,  because  the  board  is  practically  converted  into  two 
levers  whose  power-arms  remain  the  same,  but  whose 
weight-arms  are  only  one-half  as  long  each. 

405.  The  Transverse  Strength  of  Timbers  Proportional  to 
the  Squares  of  their  Vertical  Thicknesses.  —  Common  experi- 
ence demonstrates  that  a  joist  resting  on  edge  is  able  to 


Strength  of  Materials. 


333 


carry  a  much  greater  load  than  when  lying  flat-wise.  If  we 
place  a  2x4  and  a  2x8,  which  differ  only  in  thickness,  on 
edge  their  relative  strengths  are  to  each  other  as  the  squares 
of  4  and  8,  or  as  16  to  64.  That  is  the  2x8,  containing  only 
twice  the  amount  of  lumber  as  the  2x4  will,  under  the  con- 
ditions named,  sustain  four  times  the  load.  The  reason  for 
this  is  as  follows :  In  Fig.  145  let  A  represent  a  2x4  and  B 
a  2x8.  In  each  of  these  cases  the  load  draws  lengthwise 
upon  the  upper  half  of  the  joist,  acting  through  a  weight- 


FIG.  145. 


© 


arm  F,  W,  ten  inches  in  length,  to  overcome  the  force  of  co- 
hesion at  the  fixed  ends,  whose  strength,  according  to  (402) 
is  ten  thousand  pounds  per  square  inch,  or  a  total  of 

2  X  2  X  10,  000  Ibs.  =  40,  000  Ibs.  in  the  2  X  *  Joist, 
and  of  2  X  4  XlO,  000  Ibs.  =  80,  000  Ibs.  in  the  2  X  8  joist, 

These  two  total  strengths  become  powers  acting  through 
their  respective  power-arms  F,  P,  whose  mean  lengths  are, 
in  the  2x4  joist,  one  inch,  and  in  the  2x8  joist,  two  inches. 

Now  we  have  (531) 

PXPA  =  WXWA, 

and  substituting  the  numerical  values,  in  the  2x4  joist, 
we  get 


4X10,000X1  = 

or  4X10,  000  =  10W, 

and  W  =  4,000. 


334  .Rural  Architecture. 

Similarly,  by  substituting  numerical  values  in  the  case 
of  the  2x8  joist  we  get 

8X10,000X2  =  WX10, 
or  16X  10,000  =  10W, 
and  W=  16,000. 

It  thus  appears  that  the  loads  the  two  joists  will  carry  are 
to  each  other  as  4,000  is  to  16,000,  or  as  1  is  to  4;  but 
squaring  the  vertical  thickness  of  the  two  joists  in  ques- 
tion we  get,  for  the  2x4  joist 


and  for  the  2x8  joist 
8X8  =  64; 

but  16  is  to  64  as  1  is  to  4,  which  shows  that  the  transverse 
strengths  of  similar  timbers  are  proportional  to  the  squares 
of  their  vertical  diameters. 

406.  The  Transverse  Strength  of  Materials  Diminishes  Di- 
rectly as  the  Length  Increases.  —  It  will  be  readily  seen  from 
an  inspection  of  Fig.  145,  that  lengthening  the  pieces  of 
joists,  while  the  other  dimensions  remain  the  same, 
lengthens  the  long  arm  of  the  lever,  while  the  short  arm  re- 
mains unchanged;  and  since  the  force  of  cohesion  remains 
unaltered,  the  load  necessary  to  overcome  it  must  be  less  in 
proportion  as  the  lever  arm  upon  which  it  acts  is  increased. 
Thus,  if  the  2x8  in  Fig.  145  is  made  20  inches  long,  we 
shall  have, 

i 

PXPA  =  WXWA 

and  by  substituting  the  numerical  values  we  get 

80,000X2  =  WX20 

W  =  8,000 

instead  of  16;000;  as  found  in  (405). 


Strength  of  Materials.  335 

£C7.  The  Constants  of  the  Transverse  Breaking  Strength  of 
Wood. — Since  the  laws  given  in  404,  405,  and  406  apply  to 
all  kinds  of  materials,  it  follows  that  the  actual  breaking 
strength  of  different  kinds  of  materials  will  depend  upon 
the  cohesive  power  of  the  molecules  as  well  as  upon  the 
form  and  dimensions  of  the  body  which  they  constitute. 
The  breaking  strength  of  a  beam  of  any  material  is  always 
in  proportion  to  its  breadth,  multiplied  by  the  square  of  its 
depth,  divided  by  its  length,  or 

Breadth  X  the  square  of  the  depth 
length 

and  if  the  breadth  of  a  piece  of  white  pine  in  inches  is  4, 
its  depth  in  inches  10,  and  its  length  in  feet  10,  we  shall 
have,  taking  the  length  in  feet, 


10 


Now  if  we  find  by  actual  trial,  by  gradually  adding 
weights  to  the  center  of  such  a  beam,  that  it  breaks  at 
18,000  pounds,  including  half  its  own  weight,  the  ratio  be- 
tween this  and  forty  will  be 

18,000 
-40-  =  45°' 

and  as  this  ratio  is  always  found  for  white  pine,  when  the 
breadth  and  depth  are  taken  in  inches  and  the  length  in 
feet,  no  matter  what  the  dimensions  of  the  timbers  may  be, 
450  is  called  its  breaking  constant  for  a  center  load. 

For  other  materials  this  constant  is  different,  and  has 
been  determined  by  experiment  and  given  in  tables  in 
various  works  relating  to  such  subjects.  The  following  are 
taken  from  Trautwine. 


330  Rural  Architecture. 

408.  Breaking  Constants  of  Transverse  Strength  of  Differ- 
ent Materials. — 


WOODS. 

American  White  Ash 650  Ibs. 

Black  Ash 600  Ibs. 

American  Yellow  Birch 850  Ibs. 

American  Hickory  and  Bitter-nut 800   Ibs. 

Larch  and  Tamarack 400  Ibs. 

Soft  Maple., 7:.0  Ibs. 

American  White  Pine 4.",0  Ibs. 

American  Yellow  Pino '....   500  Ibs. 

Poplar S50  Ibs. 

American  White  Oak GOO  Ibs. 

American  Red  Oak 8107  Ibs. 

METALS. 

Cast  iron  1,5^0  to  2,700  Ihs. 

Wrought  iron,  bends  at 1, COO  to  2,000  Ibs. 

Brass  Sodlbs. 

409.  To  Find  the  Quiescent  Center  Breaking  Load  of  Mater- 
ials having  Rectangular  Cross-sections,  when  Placed  Hori- 
zontally and  Supported  at  Both  Ends. — In  placing  joists  and 
beams  in  barns  it  is  important  to  know  the  breaking  load  of 
the  timbers  used.  This  may  be  determined  with  the  aid  of 
the  following  rule  and  the  table  of  constants  given  in 
(408) : 

Rule. — Multiply  the  square  of  the  depth  in  inches  by 
the  breadth  in  inches  and  this  by  the  breaking  constant 
given  in  (408)  •  divide  the  result  by  the  clear  length  in 
feet  and  the  result  is  the  load  in  pounds. 

But  in  the  case  of  long  heavy  timbers  and  iron  beams 
one-half  of  the  clear  weight  of  the  beam  must  be  deducted 
because  they  must  always  carry  their  own  weight. 

Square  of  ) 
depth      [•  X  breadth  in  inches  X  Constant 

Breaking  load  =     "inches)         ^-r-T 

Length  in  feet. 

What  is  the  center  breaking  load  of  a  white  pine  2x1  "2 
joist  12  feet  long? 


Strength  of  Materials.  337 

Breaking -load  = Yo ~  10,8001bs. 

Da 

What  is  the  breaking  load  for  the  same  10  feet  long?  14 
feet  long?  16  feet  long?  18  feet  long?  Solve  the  same  prob- 
lems for  other  woods. 

410.  General  Statements  regarding  the  Quiescent  Breaking 
loads  of  Uniform  Horizontal  Beams. — If  the  center  quiescent 
breaking  load  be  taken  as  1,  then,  when  all  dimensions  are 
the  same,  to  find  the  breaking  load: 

(1)  When  the  beam  is  fixed  at  both  ends  and  evenly 
loaded  throughout  its  whole  length,   multiply  the  result 
found  by  (409)  by  two. 

(2)  When  fixed  at  only  one  end  and  loaded  at  the  other, 
divide  the  result  obtained  by  (409)  by  four. 

(3)  When  fixed  only  at  one  end  and  the  load  evenly 
distributed  divide  the  result  obtained  by  (409)  by  two. 

(4)  To  find  the  breaking  load  of  a  cylindrical  beam,  first 
find  the  breaking  load  of  a  square  beam  having  a  thickness 
equal  to  the  diameter  of  the  log  and  multiply  the  result  by 
the  decimal  .589. 

411.  Breaking  load    of 
Rafters. — In  finding    the 
breaking  load  of  timbers 
placed  in  an  oblique  posi- 
tion,   as    shown    in    Fig. 
146,  take  the  length  of  tl 

rafter  equal  to  the  hori-     u  FIG.  146. 

zontal  span  A,  C,  and  pro- 
ceed as  in  (409)  and  (410). 

412.  Table  of  Safe  Quiescent  Center  Loads  for  Horizontal 
Beams  of  White  Pine  Supported  at  Both  Ends. — In  this  table 
the  safe  load  is  taken  at  one-sixth  of  the  theoretical  break- 
ing load.  This  large  reduction  is  made  necessary  on  account 
of  the  cross-grain  of  timbers  and  joists  and  the  large  knots 


338 


Rural  Architecture. 


which  weaken  very  materially  the  pieces.  Where  a  judi- 
cious selection  is  made  in  placing  the  joists,  laying  the  in- 
herently weak  pieces  in  places  where  little  strain  can  come 
upon  them,  much  saving  of  lumber  may  be  made. 


KOOOOJ*.  Depth  in 
inches. 

Span  10  feet. 
Breadth. 

Span  12  feet. 
Breadth. 

Span  14  feet. 
Breadth. 

Span  16  feet. 
Breadth. 

2  in. 

4  in. 

6  in. 

2  in. 

4  in. 

6  in. 

2  in. 

4  in. 

6  in. 

2  in. 

4  in. 

6  in. 

Ibs. 
450 
1,008 
1,800 
2,808 
4,050 

Ibs. 
240 
540 
960 
1,500 
2,160 

Ibs. 

1,0*0 
1,920 
3,000 
4,320 

Ibs. 
720 
1,620 
2,880 
4,500 
6,480 

Ibs. 
200 
450 
800 
1,250 
1,800 

Ibs. 
400 
900 
1,600 
2.50J 
3,600 

Ibs. 
600 
1,350 
2,400 
3,750 
5,400 

Ibs. 
17;? 
386 
686 
1,072 
1,544 

Ibs. 
344 
772 
1,372 
2,144 
3,088 

Ibs. 
516 
1,158 
2,058 
3,216 
4.63J 

Ibs. 
150 
336 
600 
S36 
1,350 

Ibs. 
300 
672 
1,200 
1,872 
2,700 

fc 

8.. 
10.. 

Breadth. 

Breadth. 

Breadth. 

Breadth. 

4  in. 

10  in. 

12  in. 

8  in. 

10  in. 

Ibs. 
1,000 
2,250 
4,000 
6,250 
9,000 

12  in. 

Ibs. 
1,200 
2,700 
4,{;00 
7,500 
10,800 

Sin. 

10  in. 

12  in. 

Sin. 

10  in. 

12  in. 

Ibs. 
960 
2,160 
3,840 
6,000 
8,640 

Ibs. 
1,200 
2.70U 
4,800 
7,500 
10,800 

Ibs. 
1,440 
3,240 
5,760 
9,000 
12,960 

Ibs. 
800 
1,800 
3,200 
5,000 
7,200 

Ibs. 
688 
1,544 
2,  744 

4,288 
6,176 

Ibs. 
860 
1,930 
3,430 
5,360 
7,720 

Ibs. 
1,032 
2,316 
4,116 
6,  432 
9,264 

Ibs. 
600 
1.3J4 

2,400 

5^400 

Ibs. 
750 
l,6fcO 
3,000 

e!750 

Ibs. 
900 
2,000 
3,610 
5,601 
8,166 

413.  Selection  of  Lumber  to  Increase  Carrying  Capacity. — 
It  is  possible  to  greatly  increase  the  carrying  capacity  of  a 
lot  of  joists  or  of  a  set  of  beams  by  giving  attention  to  the 
lumber  used,  selecting  the  evidently  strongest  pieces  for  use 
where  it  is  known  the  heaviest  strains  will  come.     Some- 
times a  joist  should  be  reversed  or  turned  the  other  side  up 
in  order  to  enable  the  piece  to  render  its  highest  service. 
In  the  arrangement  of  joists  under  a  hay  bay  or  granary, 
where  heavy  loads  are  to  be  carried,  the  cross-grained  pieces 
and  those  with  exceptionally  large  knots  should  be  well  dis- 
tributed among  the  stronger  ones,  making  the  evidently 
weak  come  between  those  evidently  above  the  average  in 
strength. 

414.  Braces — There  are  two  principles  underlying  the 
use  of  braces  to  give  greater  strength  to  lumber.   (1)   That 
of  equalizing  the  load,  making  it  fall  more  heavily  upon 


Construction  of  Barn  Frames.  339 

the  stronger  members.  (2)  That  of  shortening  the  free 
span. 

The  first  case  is  illustrated  in  the  rows  of  bridging  used 
between  the  joists  in  a  floor.  In  these  cases  when  a  weak 
member  is  bridged  between  two  stronger  ones  a  portion  of 
its  load,  because  it  yields  soonest,  is  thrown  by  the  bridging 
upon  the  stronger,  and  stiffer  floors  are  thus  secured  and 
the  breaking  of  individual  pieces  prevented. 

Braces  in  nearly  all  cases  are,  in  principle,  either  posts 
or  else  they  are  suspension  rods  which  allow  the  strength  of 
the  material  to  be  utilized  unaffected  by  the  principle  of 
leverage,  the  stress  being  a  direct  pull  or  a  push,  bringing 
into  play  the  full  tensile  or  crushing  strength  of  the  ma- 
terial. 

To  shorten  the  free  span  of  an  18-foot  joist  or  timber 
two  feet  at  each  end  by  means  of  suitable  braces  is  in- 
creasing its  carrying  power  28.5  per  cent. 

It  is  much  more  important  to  pay  strict  attention  to  these 
matters  of  strength  at  the  present  time  than  in  former  years 
both  because  lumber  is  higher  and  often  of  much  inferior 
quality. 

415.  Constructing  Timbers  from  Two-inch  Lumber. — It  is 
often  not  only  cheaper  but  better  to  construct  8x10  or  8x12 
beams  by  putting  together  2x10  or  2x12  plank,  the  timber 
thus  constructed  often  being  stronger  than  a  solid  one  would 
be  because  weak  places  are  more  likely  to  be  distributed  so 
as  to  give  a  greater  mean  strength.  It  is  of  course  not  true 
that  a  10x10  so  made  would  be  stronger  than  a  solid  timber 
of  the  same  dimensions  if  both  were  of  highest  grade 
lumber. 

416.  Form  of  Barn  Frame. — During  pioneer  days,  when, 
saw  mills  were  none  or  few,  it  was  much  easier  to  secure  the 
needed  stability  for  a  barn  by  hewing  a  few  heavy  timbers 
of  suitable  length  and  putting  them  together  with  braces 
than  it  was  to  use  the  2  inch  lumber  now  so  common  in  the 
frames  of  dwelling  houses. 

Since  the  old  type  of  barn  frame  was  depended  upon  to 


340 


Rural  Architecture. 


give  the  needed  stability,  little  or  no  support  coming  from 
the  siding  or  sheeting,  it  was  necessary  to  use  large  timbers 


FIG.  147. 


and  to  frame  them,  together  and  brace  them  very  securely 
making  a  structure  costly  both  in  material  and  labor. 

417.  Plank  Frame — The  high  price  of  lumber  has  led  to 
an  effort  to  imitate  the  construction  of  the  old  hewn  timber 
frame  barn  in  the  construction  of  essentially  the  same  type 
of  frame  but  using  plank  spiked  together  instead  of  tim- 
bers.    This  type  of  frame  is  represented  in  Fig.  147. 

The  frame  so  made  is  strong  and  not  as  expensive  as  one 
of  heavy  timbers  at  the  present  prices  but  it  is  neither  aa 
simple  in  construction  nor  as  cheap  as  a  frame  for  most 
barns  can  be  made.  Now  that  the  conditions  which  made 
the  heavy  timber  frame  a  necessity  have  disappeared  there 
is  no  need  of  imitating  it  by  splicing  lumber. 

418.  Balloon  or  House  Frame — The  reason  for  not  ad- 
hering to  the  old  type  of  barn  frame  is  because  it  permits 
of  no  advantage  being  taken  of  the  inherent  strength  of  the 


Construction  of  Barn  Frames. 


341 


siding  and  sheeting  to  give  the  barn  its  needed  ability  to 
withstand  wind  pressure. 

When  the  -two  inch  lumber  used  in  the  plank  frame  is 
treated  as  studding  and  the  siding  and  sheeting  are  put  on 
horizontally,  and  securely  nailed,  the  whole  covering  of  the 
barn  then  braces  it  from  all  sides  and  does  double  duty  by 
largely  dispensing  with  braces.  To  distribute  the  plank, 
using  them  as  studding  rather  than  building  them  into 
timbers  forming  bents,  does  not  give  them  less  power  to 
withstand  pressure  from  within  or  without  and  much  less 
lumber,  less  nails  and  less  labor  are  required. 

Where  the  building  is  long  and  broad  so  as  to  require  the 
sides  to  be  tied,  bents  may  be  used  and  made  in  the  ordinary 
way  except  that  less  lumber  need  be  used  at  the  walls. 

419.  The  Eound  Barn  Frame — The  strongest  possible 
structure  for  a  barn,  with  the  least  amount  of  lumber  in  its 
frame  and  the  least  special  attention  to  bracing,  is  secured 


FIG.  148.— Showing  frame  and  general  plan  for  a  cylindrical  barn.  A. 
barn  floor  extending  around  the  silo;  B,  hay  bay;  C,  granary;  and 
T,  tool  room. 

22 


842 


Rural  Architecture. 


when  the  barn  is  made  cylindrical  in  form  and  the  studding 
set  upon  the  circumference  of  a  circle  as  represented  in 
Figs  148  and  149.  In  this  type  of  barn  not  only  is  the 
smallest  number  of  studding  required  to  form  the  outer 


FIG.   149.— Showing   frame   and   general    plan    of   a    cylindrical    barn.    A, 
driveways  behind  cattle;  B,  feed  alley;  C,  platforms  for  cattle. 

part  of  the  frame  but  smaller  sizes  can  be  used,  for  the 
reason  that  every  board  in  the  siding  is  a  portion  of  a  hoop 
which  makes  spreading  impossible,  while  at  the  same  time 
they  are  arched  against  the  wind  and  take  its  pressure  with 
a  crushing  stress. 

With  barns  of  this  type  2x4  studding  set  2  feet  apart 
have  ample  strength  for  all  diameters  up  to  40  feet  and  2x6 
studding  is  large  enough  for  barns  40  to  100  feet  in  diam- 
eter. 


CHAPTER  XVII. 
WARMTH,  LIGHT  AND  VENTILATION. 

CONTROL  OF  TEMPEBATUBE. 

The  life  activities  manifested  in  the  animal  body  involve 
the  continuous  maintenance  of  a  train  of  chemical  changes 
which  give  rise  to  or  maintain  them.  These  chemical 
changes,  like  all  others,  can  only  begin  at  a  certain  tem- 
perature; below  this  they  cease;  within  a  certain  range  they 
go  forward  at  normal  rates;  above  this  temperature  reac- 
tions occur  which  interfere  with  the  life  activities,  making 
them  abnormal  or  causing  them  to  cease. 

420.  Automatic   Control  of   Temperature. — The   animal 
body  is  so  constituted  that  within  certain  limits  the  normal 
temperature  of  the  body  may  be  maintained  automatically, 
if  only  sufficient  food  is  supplied.  If  outside  conditions  are 
such  as  to  lower  the  temperature  of  the  body  the  nervous 
system  reacts,  setting  in  operation  a  train  of  changes  which 
evolve  heat  fast  enough  to  meet  the  greater  loss.     If  on  the 
other  hand  the  surrounding  temperatures  are  too  high  and 
the  body  is  becoming  too  warm  the  heat  producing  reac- 
tions are  inhibited  or  perspiration  is  stimulated  to  reduce 
the  too  high  temperature  by  bringing  the  blood  to  the  skin, 
where  the  temperature  may  be  lowered  by  the  evaporation 
of  water  in  the  same  manner  that  the  wet  bulb  of  a  ther- 
mometer is  cooled  by  the  loss  of  heat  which  does  the  work 
of  evaporation. 

421.  Normal  Animal  Temperatures. — The  normal  temper- 
atures which  must  be  maintained  within  the  animal  body 


344  Rural  Architecture. 

vary  with  different  species  of  animals  but  among  the  warm 
blooded  forms  the  range  is  not  wide,  as  indicated  in  the 
table  below. 

Horse 100.4°F.  tol00.8°F.    ) 

Cattle 101.8  to  102 

Sheep 101.3  to  105.8  probably  103.8  to  104.4 

Swine 100.9  to  105.4 

Dog 99.5  tol01.7 

Any  marked  departure  from  these  temperatures  in  the 
animal  body,  either  up  or  down,  results  in  physiological 
disturbances  which  injure  the  health  of  the  animal. 

422.  Best  Stable  Temperature. — The  data  for  a  rational 
practice  with  reference  to  this  point  have  yet  to  be  de- 
termined experimentally.  At  present  rules  can  be  formu- 
lated only  from  general  considerations. 

Since  most  of  the  bodily  functions  result  in  the  genera- 
tion of  more  or  less  heat  and  since  the  temperature  must  be 
kept  below  100°  to  105°  it  is  clear  that  no  active  animal 
should  be  surrounded  by  temperatures  as  high  as  the  nor- 
mal temperature  of  the  body.  One  of  the  main  objects  of 
.the  circulation  of  the  blood  through  the  skin  is  to  lower  its 
temperature  before  it  returns  to  the  interior,  so  that  those 
parts  may  be  cooled.  In  our  case  we  become  uncomfortable 
in  a  surrounding  temperature  much  above  72°  and  the 
same  is  true  of  our  domestic  animals. 

Stables  should  then  as  a  rule  have  a  temperature  lower 
than  72°  F.  but  how  much  must  depend  upon  circum- 
stances. The  right  surrounding  temperature  is  that  which 
will  permit  the  necessary  loss  of  heat  from  the  body  with 
only  the  normal  rate  of  perspiration. 

Reasoning  from  general  principles  it  is  to  be  anticipated 
that  animals  which  are  being  fed  heavily,  like  fattening 
swine,  steers  or  sheep,  as  well  as  milch  cows,  will  do  better 
in  somewhat  cooler  quarters  because  (1)  the  larger  activity 
necessary  to  produce  the  extra  assimilation  desired  would 
develop  more  heat  which  must  be  removed  from  the  body, 
and  (2)  because  the  aim  is  to  induce  such  animals  to  eat  as 


Control  of  Temperature.  345 

f     '  • 

much  as  they  can  convert  economically  into  flesh  and  milk 

and  warm  quarters  must  make  the  demand  for  food  less. 

It  has  been  found  with  man  that  when  fasting  and  at  rest 
under  a  temperature  of  90°  F.  he  consumed  1,465  cubic 
inches  of  oxygen  per  hour,  but  under  the  same  conditions 
except  a  temperature  of  59°  F.  the  amount  of  oxygen  was 
13  per  cen^.  greater  and  the  amountof  carbon  dioxide  given 
off  also  13  per  cent,  greater,  showing  that  a  higher  rate  of 
consumption  of  food  in  the  body  was  maintained  and  hence 
that  the  man  would  be  required  to  eat  more. 
"  It  is  with  the  cow  and  fattening  animals  as  it  is  with  a 
threshing  machine,  it  requires  a  higher  rate  of  waste  of 
energy,  to  run  the  machine  rapidly  than  it  does  to  run  it 
slower,  but  the  saving  in  time  of  all  employed  to  manage 
the  machine  more  than  pays  for  the  greater  waste.  So  the 
cow  may  require  an  extra  amount  of  food  for  temperature 
maintenance  to  overcome  the  cooler  quarters  but  she  is 
likely  to  eat  enough  more  food  to  enable  her  to  make  more 
milk  and  a  higher  profit  when  all  items  of  expense  are  taken 
into  account. 

With  animals  on  simply  a  maintenance  ration  the  aim  is 
to  carry  them  with  the  least  amount  of  food  and  hence  in  as 
warm  quarters  as  will  be  healthful. 

It  seems  likely  that  the  best  temperature  surroundings 
for  animals  being  crowded  will  be  found  between  40°  and 
50°  F.  and  for  animals  upon  maintenance  rations  from  50° 
to  65°  or  even  70°  F. 

423.  Heat-Proof  Construction  Impossible, — £To  enclosure 
or  building  can  be  so  constructed  that  all  the  heat  it  con- 
tains will  be  prevented  from  escaping.  If  it  is  kept  above 
freezing  through  cold  winters  there  must  be  within  the  en- 
closure a  source  of  heat.  So,  too,  no  enclosure  or  building 
can  be  so  thoroughly  made  as  to  exclude  all  heat  and  hence 
it  is  impossible  to  build  a  "cool  room"  which  will  not  get 
warmer  during  the  summer  unless  it  contains  some  means 
of  removing  the  heat  which  enters. 

The  out-door  root  cellar  which  does  not  freeze  during 


346  Rural  Architecture. 

the  winter  is  prevented  from  doing  so  by  the  heat  which 
enters  it  through  the  bottom.  The  same  cellar  during  the 
summer  grows  gradually  warmer  as  the  season  advances 
and  is  only  relatively  cool  because  part  of  the  heat  entering 
above  is  conveyed  through  the  bottom  into  the  earth,  to  re- 
store that  which  kept  the  cellar  from  freezing  during  the 
winter.  The  warm  stable  which  does  not  freeze  is  kept  so 
by  the  heat  of  the  animals  sheltered,  and  the  warmly  con- 
structed stable  only  makes  less  animal  heat  needed  to  main- 
tain the  temperature ;  the  walls  in  themselves  are  not  warm. 
So,  too,  no  garment  however  made  is  in  itself  warm.  We 
call  it  warm  when  the  loss  of  heat  through  it  is  slow. 

424.  Means  of  Controlling  Temperature. — When  it  is  de- 
sired to  construct  a  room  which  will  be  warm  in  winter  or 
one  which  will  be  cool  in  summer  the  same  principles  must 
be  employed  in  each.      In  the  first  case  it  is  desired  to  re- 
tain the  heat  produced  in  the  room;  in  the  second  ca^e  to 
prevent  heat  coming  through  the  same  walls,  but  from  the 
opposite  direction. 

To  secure  either  of  these  ends  two  essentials  of  construc- 
tion must  be  observed.  The  walls  must  be  as  nearly  air 
tight  and  as  poor  conductors  of  heat  as  possible.  In  i.. 
construction  of  a  warm  house,  a  warm  stable,  a  cool  ice 
house  or  a  cool  curing  room  for  cheese  the  greatest  attention 
should  be  paid  to  securing  air  tight  walls  because,  no  mat- 
ter how  poor  conductors  are  put  into  the  walls,  if  there  are 
cracks  about  doors  and  windows  or  open  joints  in  the  wall, 
the  effect  of  wind  pressure  and  wind  suction  will  be  tc 
change  the  air  in  the  room  so  rapidly  that  it  will  be  (diffi- 
cult to  keep  it  either  warm  or  cold. 

425.  Solid  Masonry  Walls. — Stone  basements  with  solid 
walls  are  sufficiently  warm  for  stables  but  they  are  too  good 
conductors  of  heat  to  be  suitable  for  dwelling  houses  in  cold 
climates  where  the  inside  temperature  must  be  maintained 
at  72°  F.    Hollow  brick  walls,  when  plastered  with  a  close 
textured  mortar,  through  which  air  cannot  pass  readily,  are 


Control  of  Temperature.  347 

better  than  solid  masonry  but  are  not  as  warm  as  those  well 
constructed  of  all  wood  and  good  building  paper. 

An  unplastered  brick  wall,  or  a  brick  wall  plastered  with 
coarse  limie  mortar  only,  is  one  of  the  poorest  which  can  be 
used  either  to  retain  or  exclude  heat.  Its  pores  are  so  open 
that  the  smallest  wind  pressure  or  wind  suction  causes  a 
ready  flow  of  air  through  every  portion  of  the  wall, 
changing  the  air  of  the  room  quickly. 

For  cheese  curing  rooms,  where  the  temperature  is  to  be 
held  down  by  means  of  cold  air  ducts,  masonry  walls,  even 
when  made  air  tight,  are  not  suitable  because  they  are  such 
good  conductors  of  heat  and  so  massive  that  they  tend  to 
maintain  a  uniform  temperature  in  summer  somewhat 
higher  than  the  mean  of  the  air  outside. 

426.  Hollow  Masonry  Walls. — When  stone  or  brick  walla 
are  made  hollow  they  become  much  warmer  in  winter  and 
cooler  in  summer  than  when  built  solid  because  the  air  is  a 
much  poorer  conductor  of  heat.     The  thickness  of  the  air 
space  is  not  important  and  one-half  an  inch  thick  is  prac- 
tically as  serviceable  as  one  of  6  inches. 

Where  basement  or  semi-basement  curing  rooms  for 
cheese  are  constructed  the  upper  four  feet  of  the  wall 
should  be  made  with  a  dead  air  space  to  prevent  the  heat  of 
the  warm  soil  as  readily  reaching  the  interior.  So,  too,  in 
the  case  of  dwelling  houses  in  cold  climates,  whether  they 
have  cellars  under  them  or  not,  it  is  important  to  make  the 
upper  3  or  4  feet  of  the  wall  hollow  for  the  reason  that  the 
cellar  will  be  warmer  and  hence  the  floors  under  the  living 
rooms  above. 

427.  Brick  Veneered  Walls. — Where  brick  are  cheap  and 
lumber  high,  walls  made  of  2x4  studding  sheeted  inside 
and  outside  with  matched  fencing  and  then  veneered  with 
brick  make  a  very  durable  and  warm  building.     The  brick 
will  not  decay  and  the  expense  of  nails  and  frequent  paint- 
ing are  avoided. 

It  does  not  do  to  depend  upon  the  brick  for  warmth,  how- 


34:8  Rural  Architecture. 

ever;  they  simply  take  the  place  of  the  siding  and  paint. 
"Where  the  house  is  simply  sheeted  outside  with  common 
boards  and  veneered  with  brick,  and  then  lathed  and 
plastered  inside,  the  building  will  be  very  cold  because  the 
wind  will  go  easily  through  the  brick  and  the  cracks  in  the 
sheeting. 

i 

428.  All  Wood  Walls. — For  the  construction  of  dwelling 

houses,  cheese  curing  rooms  above  ground  and  ice  houses 
there  is  no  type  of  wall  so  effective  and  so  cheap  in  first 
cost  as  the  all  wood  wall  where  good  building  paper  is  used 
with  the  lumber.  For  a  dwelling  house  a  reasonably  warm 
:wall  is  secured  when  the  studding  are  sheeted  outside  and 
in  with  one  layer  of  tongued  and  grooved  fencing,  covered 
outside  with  2-ply  acid  and  waterproof  paper  and  lathed 
and  plastered  inside.  The  inside  sheeting  is  warmer  than 
back  plastering  and  better  because  it  gives  a  more  solid 
wall,  and  lath  may  be  used  on  it  for  furring. 


LIGHTING  FAEM  BUILDINGS. 

The  lighting  of  farm  buildings  is  required  to  secure 
three  important  objects:  (1)  facility  in  doing  work;  (2) 
needs  of  the  animals  housed,  and  (3)  healthful  conditions. 

In  the  dwelling  house  much  care  should  be  exercised  to 
secure  an  ample  amount  of  light  in  the  kitchen,  in  the 
dining  room  and  especially  in  the  main  living  rooms.  An 
abundance;  of  light  is  needed  in  the  kitchen  not  only  to 
facilitate  the  work  but  to  make  the  best  intentions  and 
efforts  toward  cleanliness  more  certain.  It  requires  an 
effort  to  be  gloomy  and  feel  ugly  in  the  face  of  a  hearty 
laugh,  and  a  bright  cheerful  room  has  much  the  same  effect 
upon  those  who  occupy  it. 

429.  Efficiency  of  Windows. — There  are  many  conditions 
which  affect  the  efficiency  of  windows  in  lighting  a  build- 


Lighting  of  Farm  Buildings.  349 

ing.  Trees  or  buildings  near  by,  which  cover  a  consider- 
able portion, of.  the  sky,  may  reduce  the  light  entering  a 
window  very  much.  Much  more  light  comes  from  the 
sky  high- above  the  horizon  than  from  low  down  and  hence 
a  porch  over  a  window  cuts  out  a  very  large  share  of  the 
light  which  might  enter  it. 

Buildings  which  have  thick  walls  require  larger  win- 
dows to-  admit  the  same  amount  of  light  as  would  enter 
through  windows  in  thin  walls.  Basement  stables  with 
heavy  stone  walls  require  larger  windows  because  the  walls 
are  thick,  and  so  with  a  brick  or  stone  house. 

Windows  long  up  and  down  admit  much  more  light 
thafr  windows  of  the  same  dimensions  with  their  long  axis 
horizontal  because  much  more  light  comes  from  the  upper 
portion  of  the  sky.  So,  too,  windows  extending  from  near 
the  ceiling  toward  the  floor  light  the  room  better  than 
when  extending  from  near  the  floor  up. 

430.  Position  of  Windows — Living  rooms  and  stables 
should  if  possible  be  arranged  so  that  the  body  of  light 
may  come  from  the  south  side  where  the  direct  sunshine 
may  enter  the  windows.  In.  a  dwelling  house  in  the  win- 
ter this  is  very  important  because  then  the  amount  of  light 
is  smallest  at  best  and  the  family  must  be  more  closely 
confined  and  therefore  need  the  direct  sun  then  most.  For 
poultry  and  for  swine  south  windows  are  specially  de- 
sirable. Large  windows  at  the  south  are  not  as  objec- 
tionable for  heat  in  summer  as  might  at  first  be  thought 
because  the  sun  is  so  high  that  a  large  portion  of  the  direct 
sunshine  is  reflected  from  the  glass  and  prevented  from 
entering  the  house ;  but  during  the  winter,  when  the  sun  is 
low,  the  advantage  which  comes  from  its  heating  effect  as 
Well  as  the  light  is  very  considerable^ 


•50  Rural  Architecture. 


VENTILATION  OF  FARM  BUILDINGS. 

In  the  physiological  sense  air  is  as  indispensable  to  the 
cow  and  horse  as  is  water,  grain,  hay  or  grass]  so,  too,  is  it 
as  essential  to  the  development  of  power  in  the  steam 
engine  as  is  the  water  and  the  fuel.  It  is  so  abundant  about 
us  and  we  procure  it  usually  so  unconsciously  that  its 
necessity  does  not  occur  to  us.  But  when  large  numbers 
of  animals  are  housed  together  in  close  stables  ample  pro- 
vision must  be  made  for  the  ingress  and  egress  of  air. 

431.  Necessity  for  Ventilation. — The  need  of  ventilating 
dwellings  and  stables  grows  out  of  several  conditions:  (1) 
The  consumption  of  the  oxygen  which  is  the  essential  in- 
gredient;   (2)   the  exhalation  from  the  lungs  of  carbon 
dioxide,  moisture,  ammonia,  marsh  gas  (C  H4)  and  organic 
matter;  (3)  the  accumulation  in  the  air  of  occupied  stables 
and  dwellings  of  bacteria  and  other  micro-organisms  as 
well  as  solid  dust  particles. 

432.  Carbon  Dioxide  in  the  Air. — This  gas  is  given  off 
from  the  lungs  with  each  respiration  in  nearly  the  same 
ratio  that  the  oxygen  is  removed,  hence  air  once  breathed 
is  not  only  deprived  of  a  portion  of  its  oxygen  but  it  is  di- 
luted with  an  equal  volume  of  carbon  dioxide  and  is  there- 
fore rendered  doubly  unfit  for  use  again. 

That  air  once  breathed  from  the  lungs  is  not  suited  to 
further  use  can  be  clearly  and  forcibly  proved  by  filling 
a  quart  Mason  jar  with  air  from  the  lungs,  by  blowing 
through  a  rubber  tube,  and  then  quickly  lowering  a  lighted 
taper  into  it,  which  is  quickly  extinguished,  showing  that 
the  air  has  lost  so  much  oxygen  and  gained  so  much  carbon 
dioxide  that  the  taper  cannot  burn  in  it. 

433.  Moisture  from  the  Lungs  and  Skin. — The  moisture 
taken  with  the  food  and  as  drink  must  be  again  removed 


Ventilation  of  Farm  Buildings.  351 

from  the  body  and  a  large  portion  of  it  leaves  through  the 
lungs  and  skin  in  the  form  of  invisible  vapor.  If  the  air 
of  a  stable  or  dwelling  is  not  changed  with  sufficient  fre- 
quency it  becomes  so  damp  as  to  interfere  with  the  proper 
action  of  the  lungs  and  skin  in  this  respect,  and  it  is  im- 
portant that  the  ventilation  should  be  strong  enough  to 
prevent  the  air  becoming  too  damp. 

One  of  the  surest  indications  of  an  improperly  venti- 
lated stable  is  the  condensation  of  moisture  on  the  walls, 
ceiling  and  floors.  It  is  sometimes  remarked  that  cement 
floors,  and  stone  basements  are  objectionable  because  they 
"draw  moisture,"  making  the  air  damp.  The  truth  is  the 
stables  are  insufficiently  ventilated  and  the  moisture  from 
the  animals  condenses  upon  the  cement  floor  and  stone 
walls  simply  because  these  happen  to  be  colder.  Instead 
of  "drawing"  moisture  and  making  the  air  damp  they  have 
exerted  exactly  the  opposite  effect  by  condensing  the 
moisture  from  the  air,  leaving  it  dryer  than  if  the  con- 
densation had  not  occurred. 

434.  Ammonia  and  Organic  Matter  Removed  from  the 
Lungs. — When  one  passes  from  the  fresh  air  into  an  occu- 
pied stable  or  room  where  the  air  has  been  rendered  im- 
pure from  imperfect  ventilation  a  depressed  feeling  and 
offensive  odor  are  recognized  and  sometimes  this  effect  may 
be  so  strong  as  to  produce  nausea.  When  these  odors  and 
the  odor  of  ammonia  can  be  detected  it  is  positive  proof 
that  the  air  needs  changing  more  rapidly. 

Some  of  the  organic  matter  given  off  from  the  lungs  is 
strictly  poisonous  and  so  much  so  as  to  produce  death  in  a 
few  moments.  If  a  live  mouse  is  kept  in  a  sealed  pint  fruit 
jar  until  it  is  nearly  suffocated,  as  shown  by  its  action, 
another  mouse  introduced  into  this  jar  will  die  at  once, 
while  the  one  which  vitiated  the  air  may  be  removed  and 
it  will  apparently  recover.  It  appears  as  if  the  organic 
principle  eliminated  from  one  animal  is  more  poisonous 
when  breathed  by  another,  even  of  the  same  kind. 


352  Rural  Architecture. 

So  poisonous  is  the  organic  principle  removed  from 
the  lungs  that  Brown-Sequard  in  1887  condensed  the 
vapor  of  expired  air  and  injected  15  cc.  of  it  into  a  rabbit 
which  died  from  the  effects.  Brown-Sequard  considered 
the  substance  a  volatile  alkaloid  secreted  by  the  lungs. 

Water  standing  over  night  in  a  poorly  ventilated  room 
or  stable  comes  to  have  a  very  disagreeable  taste  from  the 
absorption  of  impurities  from  the  air  and  this  is  one  of  the 
most  serious  objections  to  keeping  water  standing  in  the 
Btable  for  cows  or  other  animals. 

435.  Micro-organisms  and  Dust  in  the  Air — It  has  long 
been  recognized  that  the  air  of  old  and  poorly  ventilated 
houses,    especially    if    they  are  not  kept  clean,  contains 
many    more    dust    particles,  spores  and  micro-organisms 
than  newer  and  better  ventilated  houses  do.       The  same 
must  be  true  also  of  stables  but  in  a  higher  degree.     The 
amount  of  dust  and  of  organisms  as  well  is  almost  always 
more  abundant  in  occupied  rooms  than  in  the  open  air. 
This  would  be  expected  both  because  of  the  slowing  down 
of  air  movements  after  entering  the  house,  which  acts 
exactly  like  a  silt  basin  in  a  line  of  tile,  and  because  of 
their  production  there  from  various  causes. 

Strong  ventilation  tends  to  remove  these  organisms  and 
dust  particles  with  the  air  from  the  compartments  and 
this  is  the  rational  basis  for  airing  a  bedroom  or  any  other 
after  sweeping.  The  air  has  been  filled  with  both  sets  of 
impurities  and  opening  the  windows  or  using  any  other 
means  of  producing  a  strong  current  will  help  to  clear  the 
room. 

436.  Bad  Ventilation  Predisposes  to  Disease The  most 

helpful  health  rule  which  man  can  adopt  for  himself  or 
for  his  domestic  animals  is  to  avoid  whatever  tends  to 
weaken  the  system  and  to  take  advantage  of  whatever 
tends  to  greater  vigor. 


Ventilation  of  Farm  Buildings.  353 

It  should  be  cleaily  recognized  that  the  germs  of  diph- 
rtheria,  of  tuberculosis,  hog  cholera  and  other  contagious 
diseases  are  liable  to  be  met  with  almost  any  day  and  in 
any  place  and  that  wherever  a  proper  breeding  place  may 
be  found  the  disease  is  liable  to  start  and  from  it  spread  by 
force  of  greater  numbers  of  germs. 

While  therefore  the  micro-organisms  usually  found  in 
greatest  numbers  in  dusty  houses  and  stables  poorly  venti- 
lated and  cared  for  are  not  in  themselves  a  source  of  dan- 
ger, the  run-down,  weakened  condition  which  poor  ventila- 
tion is  sure  to  engender  will  certainly  tend  to  start  a  case 
of  contagious  disease  and  then,  with  greater  numbers  of 
germs  in  the  air  to  be  introduced  into  the  system,  animals 
of  greater  vigor  must  succumb  to  these  invisible  foes  be- 
cause of  their  vast  numbers. 

Ample  ventilation  then  should  always  be  secured,  first, 
as  an  indispensible  condition  for  maintaining  the  power 
to  resist  disease,  and  second,  in  case  of  disease,  to  both  clear 
the  air  and  to  give  the  animals  an  opportunity  to  defend 
themselves  against  this  type  of  foe. 

437.  Amount  of  Air  Respired. — The  amount  of  air  ordi- 
narily taken  into  and  put  out  of  the  lungs  by  man  with 
each  respiration  is  given  by  different  observers  as  follows: 

Herbst 20   —  30  cubic   nches 


Valentin    14    —  92  cubic 

Vierordt 10    —42  cubic 

Coathupe 16  cubic 


nchea 
nches 
nchos 


Ilutchinson 16    —  20  cubic  inches 

Average 15.2  —  46  cubic  inches 

or  an  average  of  about  30  cubic  inches. 

The  amount  of  pure  air  which  must  be  breathed  in  order 
to  supply  the  oxygen  needed  by  different  animals,  deduced 
from  Colin's  table,  is  given  below: 


154: 


Rural  Architecture. 


ANIMAL. 

AIR  BREATHED  IN 
24  HOURS. 

OXYGEN  CONSUMED  IN 
24  HOURS. 

Per  1,000 
Ibs.  of 
weight. 

Per  head. 

cu.  ft. 
425 
3,401 
2,*04 
1,  10.J 
726 
24.84 

Per  1,000 
Ibs.  of 
weight. 

Per  head. 

Man       

cu.  ft. 
2,833 
3,401 
2,  C0t 
7,353 

Ibs. 

12.207 
13.272 
11  04 
29.65)8 
29.314 
24.84 

Ibs. 

1  Ml 
13  ^72 
11  01 
4.456 
2.931 
.075 

Cow.           

7,259 

8,278 

Hen.                    

438.  Amount    of    Air    Used    Compared    with    Feed    and 
Water. — A  1,000-pound  cow  requires  daily  the  equivalent 
of  about  30  Ibs.  of  hay  and  grain  and  70  Ibs.  of  water  or, 
in  round  numbers,  100  Ibs.  per  head  and  per  day  of  solid 
and  liquid  food. 

A  cubic  foot  of  air  weighs  about  .08  Ibs.  hence,  from 
the  table  in  (437),  we  have 

2804  X  -08  Ibs.  =  224.32  Ibs. 

which  shows  that  a  cow  needs  to  be  supplied  with  twice 
the  weight  of  pure  air  that  she  does  of  food  and  water  com- 
bined. 

439.  Degree  of  Impurity  of  Air  Permissible — We  are  yet 
without  sufficiently  exact  data  to  permit  this  problem  to 
be  concisely  stated  for  stables  used  for  domestic  animals. 
In  absence  of  exact  data  and  in  view  of  the  unavoidable 
leakage  of  air  through  the  walls  and  about  windows  and 
doors  we  have  arbitrarily  assumed  that  if  the  air  is  changed 
in  the  stable  ait  such  a  rate  that  it  at  all  times  contains  no 
more  than  3.3  per  cent,  of  air  once  breathed  fairly  good 
ventilation  would  be  provided. 

440.  Rate  of  Supply  of  Air  to  Stables. — On  the  basis  of 
(439)  the  number  of  cubic  feet  of  air  per  head  and  per 


Ventilation  of  Farm  Buildings. 


355 


hour,  using  the  data   in  the  table  of  (437),    would  be  as 
stated  below: 

For  horses 4, 296     en.  ft.  per  hour  per  head. 

For  cows 3,542     cu.  ft.  per  hour  per  head. 

For  swine 1,392     cu.  ft.  per  hour  per  head. 

For  sheep 917     cu.  ft.  per  hour  per  head. 

For  hens 31.4  cu.  ft.  per  hour  per  head. 


PIG.  ISO.— Simplest  method  of  taking  air  into  stone  or  basement  stable. 
A  B  and  A  B  show  where  the  air  enters.  These  flues  may  be  made 
out  of  ordinary  5  or  6  inch  stove  pipe  with  elbow,  or  galvanized  Iron 
conductor  pipe,  or  the  pipe  through  wall  may  be  ordinary  5  inch 
drain  tile,  with  stove  pipe  and  elbow  on  inside,  or  the  flue  may  be 
made  of  6  inch  fencing. 

The  weights  here  assumed  are  1,000  Ibs.  for  the  horse 
and  cow,  150  Ibs.  for  the  hog,  100  Ibs.  for  sheep  and  3  Ibs. 
for  the  hen.  With  different  weights  the  amounts  would 
change  somewhat  in  proportion  to  the  size  of  the  animals. 


441.  Capacity  of  Ventilating  Flues — With  the  data  in  the 
last  section,  and  the  number  of  animals  to  be  provided  with 
air,  the  capacity  of  ventilating  flues  should  be  such  as  to 
ensure  an  air  movement  equal  the  rate  given  in  the  table 
of  (440).  It  is  practicable  to  construct  ventilating  flues 
through  which  the  air  from  stables  will  travel  at  the  rate 
of  200  to  500  feet  per  minute  without  mechanical  forcing 
or  the  aid  of  heat,  other  than  that  derived  from  the  ani- 
mals in  the  stable. 

With  a  ventilating  flue  2x2  feet  inside  measure  20  cows 
would  be  supplied  when  the  current  in  the  flue  was  at  the 
rate  of  295  feet  per  minute.  At  this  rate  40  cows  would 


356 


Rural  Architecture. 


need  two  flues   2x2  feet  inside  measure;    60  cows  three; 
80  cows  four  and  100  cows  five. 


FIG.  151.— Modification,  of  Fig.  150  where  on  the  right  a  notch  is  left  In 
the  wall  when  building,  so  that  the  flue  rises  flush  with  tke  inside 
of  the  wall.  While  on  the  left  side  the  flue  is  shown  built  in  the  wall. 
This  may  be  done  by  building  around  5-inch  drain  tile  or  around  a 
box  made  of  fencing. 

442.  Cubic  Feet  of  Space  in  Stable  per  Animal It  haa 

been  customary  with  sanitary  engineers  in  planning  hospi- 
tals, prisons,  school  rooms,  etc.,  to  allow  so  many  cubic 
feet  of  space  per  occupant,  but  the  number  chosen  has  not 


FIG.  152.— Method  of  taking  air  into  a  bank  barn  on  the  up-hill  or  bank 
sfde.  The  air  flue  is  made  In  the  same  way  as  described  in  Figs.  150 
and  151.  but  on  the  outside  has  its  end  covered  as  represented  at  A 
on  the  right  with  a  length  of  6  or  8  inch  sewer  tile  with  its  top  cov- 
ered with  a  cap  of  coarse  wire  screen.  Drain  tile  would  not  answer 
for  the  outside  exposure  at  the  surface  of  the  ground  as  frost  would 
cause  it  to  crumble.  Wood  could  be  used  and  replaced  after  rotting 
has  occurred. 

been  to  supply  the  proper  amount  of  air  but  rather  to  avoid 
drafts  too  strong  for  health  and  comfort. 

It  should  be  distinctly  stated  that  in  matters  of  rentila- 


Ventilation  of  Farm  Buildings. 


357 


tion  it  is  cubic  feet  of  air  rather  than  cubic  feet  of  space 
which  should  be  provided,  and  in  the  construction  of  stables 
the  amount  of  space  need  be  only  so  much  as  is  required  to 
permit  ample  room  and  freedom  to  care  for  the  animals. 


FIG.  15?.— Two  methods  of  ventilating  a  dairy  barn.  On  the  right  the  ven- 
tilating flue  D  F  rises  straight  from  the  floor,  passing  out  through 
the  roof  and  rising  above  the  ridge.  One,  two,  or  three  of  these 
would  be  used  according  to  number  of  cattle.  The  flues  should  be  at 
one  or  the  other  side  of  the  cupola  rather  than  behind  it.  On  the 
left  C  E  represents  how  a  hay  shoot  may  be  used  also  for  ventilating 
flue.  In  each  of  these  cases  the  ventilating  flue  would  take  the  place 
of  one  cow.  This  method  would  give  the  best  ventilation  but  has 
the  objection  of  occupying  valuable  space.  C,  in  the  feed  shoot,  Is 
a  door  which  swings  out  when  hay  is  being  thrown  down,  but  is 
closed  when  used  as  a  ventilator,  the  door  not  reaching  quite  to  the 
floor.  To  take  air  into  this  stable  if  it  is  built  of  wood  with  studding, 
openings  would  be  left  at  A  about  4x12  inches  every  twelve  to  six- 
teen feet,  and  the  air  would  enter  and  rise  between  the  sheeting 
of  the  inside  and  the  siding  on  the  outside,  entering  at  B  as  repre- 
sented by  the  arrows.  If  the  barn  is  a  basement  or  stone  structure 
the  air  intakes  could  be  such  as  described  in  figures  150,  151.  and  152. 

Twenty  cows  should  not  be  housed  in  a  space  much  less 

than  28x33  feet,  with  ceilings  8  feet  in  the  clear.     In 

warm  climates  there  is  no  objection,  except  the  matter  of 

cost,  to  high  stables,  but  where  it  is  cold  high  ceilings  per- 

23 


358  Rural  Architecture. 

mit  the  warm  air  to  rise  so  far  above  the  animals  as  to  leave 
the  stable  cold  at  the  floor. 


443.  Forces  Which  Produce  Ventilation. — The  movement 
of  air  currents  into  and  from  a  ventilated  stable  is  caused 

1.  By  the  wind  pressure  against  the  building  tending  to 
force  air  into  the  stable. 

2.  By  wind  suction  on  the  leeward  side  of  the  stable 
tending  to  draw  air  out. 

3.  By  aspiration  across  the  top  of  the  ventilator. 

4.  By  the  difference  in  temperature  between  the  air 
in  the  stable  and  that  outside. 

When  the  wind  is  blowing  against  a  building  there  is  an 
increase  of  precsure  above  that  inside  which  forces  air  into 
the  stable  through  any  available  opening  and  then  out 
again  on  the  opposite  side  or  up  the  ventilating  flue.  At 
the  same  time  there  is  a  low  pressure  on  the  lee  side  which 
tends  to  draw  air  through  any  openings  on  that  side. 

Where  the  ventilator  rises  above  the  roof  as  a  chimney 
does  the  movement  of  air  across  its  top  produces  a  di- 
minished pressure  and  the  air  is  aspirated  out  on  the  prin- 
ciple of  the  aspirator  used  on  perfumery  bottles. 

The  difference  of  temperature  causes  a  difference  of 
pressure  because  of  the  expansion  making  the  air  in  the 
stable  relatively  lighter  than  that  outside;  and  the  longer 
the  chimney  or  ventilating  flue  the  stronger  will  be  the 
draft,  both  from  difference  of  temperature  and  the  aspi- 
ration across  the  top  of  the  chimney. 

444.  Essential  Features  of  a  Ventilating  Flue. — A  good 
ventilating  flue  must  have  all  of  the  characteristics  pos- 
sessed by  a  good  chimney.     It  should  be  constructed  with 
air-tight  walls  so  that  no  air  can  enter  except  from  the 
stable.     It  should  rise  above  the  highest  portion  of  the 
roof  so  as  to  get  the  full  force  of  the  wind.     It  should  be 
as  nearly  straight  as  practicable  and  should  have  an  ample 
cross  section.     Stronger   currents  through  the   ventilators 


Ventilation  of  Farm  Buildings. 


359 


will  be  secured  by  making  one  or  a  few  large  ones  than 
where  many  small  ones  are  provided,  and  it  is  usually  best 


FIG.  154.— Second  best  method  of  ventilating  an  ordinary  barn.  The  air 
comes  in  as  described  in  the  other  figures,  and  passes  out  through 
one  or  more  ventilators  rising  against  the  side  of  the  barn  and  pass- 
ing out  through  the  roof,  as  represented  at  A  C  E.  To  make  these 
flues  if  the  barn  is  a  balloon  frame,  the  best  method  would  be  to 
secure  the  lightest  galvanized  iron  in  eight  or  ten  foot  lengths,  and 
place  the  studding  where  the  flues  are  to  be,  the  right  distance  apart, 
so  that  a  width  of  the  metal  covers  the  space  between  two  studs. 
Sheets  of  this  metal  nailed  on  opposite  faces  of  the  stud  would  make 
an  air-tight  flue.  On  the  outside,  this  metal  would  be  covered  with 
the  siding.  On  the  inside  in  the  stable,  with  the  sheeting,  but  in 
the  barn  above  nothing  would  be  needed  except  perhaps  an  occasional 
shield  to  prevent  the  hay  from  crushing  it  in.  If  it  is  not  desired 
to  carry  the  flues  through  the  roof,  they  may  end  just  below  the 
plate,  and  the  air  pass  out  through  the  cupola.  The  method  repre- 
sented, however,  would  give  the  strongest  draft.  The  width  of  stud- 
ding used  for  the  flue  would  vary  with  the  number  of  animals  to 
be  provided  for. 


to  have  as  few  as  practicable  and  not  leave  the  air  impure 
in  distant  parts  of  the  stable. 

445.  location  of  Ventilator. — The  best  location  for  the 
ventilating  shaft  is  near  the  center  of  the  stable  where 


360 


Rural  Architecture. 


such  a  position  will  not  interfere  with  the  work.     It  is  not 
of  ten.  that  this  position  can  be  utilized,  and  when  it  can- 


FIG.  155.— Modification  of  Fig.  157,  where  the  air  passes  straight  out 
through  the  1'oof,  instead  of  being  carried  in  and  out  through  the 
ridge  of  the  roof.  This  method  would  give  a  stronger  current,  un- 
less the  ventilator  passes  straight  down  to  the  floor  between  the  cows, 
as  represented  in  Fig.  153. 

not  it  may  .be  located  in  various  places,  as  indicated  in 
Figs.  153  to  160. 

446.  Openings  to  the  Ventilator.- — The  ventilator  should 
reach  to  the  stable  floor  so  that  air  may  enter  the  shaft 
from  that  level.  This  is  very  important  because:  (1)  The 
animals  not  only  stand  and  lie  low  down  but  are  so  consti- 
tuted as  to  breathe  the  impurities  directly  to  the  floor  where 


Ventilation  of  Farm  B.iildings. 


361 


the  carbon  dioxide  tends  to  remain,  because  it,  is  heavier 
than  the  rest  of  the  air  in  the  stable,  even  although  its 
temperature  is  higher. 


FIG.  155. — Represents  a  method  of  carrying  the  flues  up  the  sides  and 
then  along  undor  the  roof  between  the  rafters,  so  as  to  reach  the 
ridge  either  under  the  cupola,  or  at  other  places  on  either  side. 
Such^a  flue  could  be  made  very  tight,  by  nailing  the  light  galvanized 
Iron  on  the  outside  and  inside  of  studding,  and  rafters,  haying  a 
sufficient  width  to  give  the  proper  capacity  for  the  ventilating  flues, 
and  such  a  system  of  ventilation  would  work  fairly  well  but  could 
not  be  expected  to  do  as  effective  service  as  the  methods  shown 
in  Figs.  153,  154,  158  and  159. 

(2)  The  coldest  air  is  at  the  floor  and  the  warmest  at 
the  ceiling  and  it  is  the  cold  air  which  should  be  removed 
during  the  winter  rather  than  the  warm. 

There  should  be  an  opening  provided  at  the  ceiling  for 
warm  air  to  escape  when  the  stable  is  too  warm  and  when 
it  is  desired  to  force  the  ventilation  at  the  expense  of  the 
heat  developed  by  the  animals. 

-'Both  of  these  openings  should  bo  provided  with  regu- 
lating valves  so  that  either  or  both  may  be  partly  or  com- 
pletely closed. 


362 


Rural  Architecture. 


447.  Entrance  for  Fresh  Air.— When  a  stable  has  been 
made  close  and  warm,  requiring  attention  to  ventilation, 
provision  must  be  made  for  air  to  enter  the  stable  as  well 
as  to  leave  it.  This  may  best  be  done  as  represented  in 
Figs.  150-153  and  158-1GO. 


IPlo.  157.— Shows  method  of  ventilating  an  ordinary  barn,  where  the  air 
is  taken  out  of  the  stable  through  flues  built  between  the  studding 
and  between  the  joists  of  the  ceiling,  the  air  then  rising,  through 
ventilating  shafts,  made  against  or  as  a  part  of  one  or  more  of  the 
purliue  posts.  The  air  enters  at  A  A  and  B,  following  the  arrows 
and  passing  out  along  the  lines  C  D  E.  These  ventilators,  if  de- 
sired, can  be  carried  out  straight  through  the  roof,  or  may  be  ter- 
minated inside  under  the  purline  plate,  or  as  represented  in  the 
figure.'  The  cross  section  at  the  right  shows  how  2xl2's  and  2x6's 
may  be  nailed  together  and  placed  so  as  to  constitute  a  purline 
post,  and  at  the  same  time  a  ventilating  flue.  The  two  sides  of  the 
purline  post  or  ventilating  flue  are  represented  closed  with  sheets 
oZ  galvanized  iron.  They  may  also  be  closed  with  well  seasoned 
matched  flooring.  The  number  of  bends  necessary  in  this  plan  is 
an  objection,  as  they  interfere  with  the  draft  more  or  less. 

In  all  of  these  cases  it  will  be  noted  that  the  fresh  air 
enters  at  the  ceiling.  This  is  for  the  purpose  of  mingling 
it  with  the  warmest  air  of  the  stable  so  as  to  raise  its  tern- 


Ventilation  of  Farm  Buildings. 


3G3 


perature  before  it  falls  to  the  floor.  In  this  way  the  heat 
which  is  wasting  at  the  ceiling  is  saved  and  the  animals 
are  prevented  from  lying  in  cold  air. 

Provision  is  further  made  for  the  air  to  enter  the  intakes 
outside  at  a  distance  of  3  or  more  feet  below  the  ceiling  so 
as  to  prevent  the  warm  air  being  drawn  out  at  these  places 
by  suction  or  to  pass  out  directly  as  it  would  if  they  opened 
directly  through  the  walls. 

These  openings  should  be  placed  on  all  sides  of  the 
stable  if  possible  so  as  to  take  advantage  of  the  wind  pres- 
sure at  all  times  in  increasing  the  draft.  It  is  better  to 
have  many  small  openings  than  a  few  large  ones  because 
the  cold  air  is  better  distributed,  lessening  drafts. 

448.  Construction  of  the  Ventilators. — The  best  form  of 
ventilating  flue  is  that  represented  in  Fig.  160,  made  of 
galvanized  iron  in  cylindrical  form.  Another  good  form  is 


FIG.  158.— Method  of  ventilating  a  lean-to  stable.  The  air  enters  as  rep- 
resented bv  the  arrows  at  A  B  and  passes  out  through  a  flue  built 
ou  the  inside  of  the  upright  or  main  barn.  This  flue  may  rise  di- 
rectly through  the  roof  or  it  may  end  at  E  as  shown  in  the  figure, 
the  air  passing  through  a  cupola.  If  the  upright  barn  has  a  bal- 
loon frame,  then  the  space  between  the  studding  could  be  used 
as  ventilating  flues  in  the  same  manner  as  described  in  Fig.  154. 
These  flues  could  be  made  tighter  by  covering  inside  and  out  on  the 
studding,  with  the  lightest  galvanized  iron. 


3G4: 


Rural  Architecture. 


represented  in  Fig.  157,  where  the  sides  are  also  made  of 
galvanized  iron. 

As  a  substitute  for  galvanized  iron  in  this  form  of  ven- 
tilating flue  a  good  roofing  paper  may  he  used,  such  as  the 
ruberoid  roofing  made  by  the  Standard  Paint  Company. 


449.  Ventilation  of  Basement  Stables. — There  is  a  general 
impression  that  basement  stables  are  necessarily  unhealth- 
ful.  This  idea  has  grown  out  of  the  fact  that  it  has  been 
possible  to  make  these  stables  much  closer  and  warmer 
than  ordinary  over-ground  forms,  and  where  ample  venti- 
lation has  not  been  provided  they  have  been  damp  and 
close. 


FIG.  159.— Method  of  ventilating  a  barn  where  a  silo  or  granary  occupies 
the  central  portion.  The  air  enters  at  A  B  and  the  ventilating  Hues 
are  the  spaces  between  the  studding  which  form  the  walls  of  the 
silo,  or  other  structure.  The  air  entering  at  C  in  openings  left  all 
around  the  silo,  and  passing  out  at  D  at  the  top. 

Where  basement  stables  are  well  lighted  and  properly 
ventilated  there  is  no  objection  to  them  on  sanitary 
grounds  and  they  have  many  points  in  their  favor  where 
the  conditions  admit  of  their  being  easily  constructed. 
Methods  of  introducing  the  air  into  these  stables  are  repre- 
sented in  Figs.  150  to  152. 


Ventilation  of  Farm  Buildings.  365 

( 

1 


FIG.  160.— Is  a  section  of  the  cow  stable  of  the  dairy  barn  at  the  Wis- 
consin Experiment  Station.  A  single  ventilating  flue  D  E  rises  above 
the  roof  of  the  main  barn,  and  is  divided  below  the  roof  into  two 
arms  A  B  D,  which  terminate  at  or  near  the  level  of  the  stable  floor 
at  A  A.  These  openings  are  provided  with  ordinary  registers,  with 
valves,  to  be  opened  and  closed  when  desired.  Two  other  ventilators 
are  placed  at  B  B,  to  be  used  when  the  stable  is  too  warm,  but 
are  provided  with  valves  to  be  closed  at  other  times.  C  is  a  di- 
rect 12-inch  ventilator  leading  into  the  main  shaft,  and  opening 
from  the  ceiling,  so  as  to  admit  a  current  of  warm  air  at  all  times 
to  the  main  shaft  to  help  force  the  draft.  This  ventilating  shaft  ia 
made  of  galvanized  iron,  the  upper  portion  being  3  feet  in  diameter. 
The  covering  on  the  outside  is  simply  for  architectural  effect. 


CHAPTEK  XVIII. 


PRINCIPLES  OF  CONSTRUCTION. 


DELATION  OF  COVERING  TO  SPACE  ENCLOSED. 

The  first  cost  of  a  building,  when  expressed  in  terms  of 
cubic  feet  enclosed,  is  influenced  much  by  its  relative  di- 
mensions. 

450.  Relation  of  Walls  to  Floor  Space. — The  form  of  floor 
space  which  can  be  enclosed  by  the  smallest  amount  of  wall 
is  a  circle,  and  Fig.  161  represents  equal  amounts  of  floor 
space  enclosed  by  the  circle,  the  square  and  the  oblong. 
If  the  circle  encloses  a  floor  space  of  1,600  square  feet  the 
length  of  the  outside  wall  will  be  about  143.7  feet;  the 
square  would  then  be  40x40  feet  and  have  160  feet  of  out- 
side wall;  wrhile  the  oblong  would  be  20x80  feet  and  have 
an  outside  wall  of  200  feet. 


144  ft.  100  ft  200  ft. 

FIG.  1C1.— Shows  equal  areas  enclosed  by  three  types  of  walls. 

The  square  which  encloses  the  same  floor  space  as  a 
circle  requires  11.44  per  cent,  more  wall,  while  the  oblong 
whose  length  is  twice  the  breadth  requires  nearly  40  per 
cent,  more  wall.  This  means  that  40  per  cent,  more  siding, 
more  nails  and  more  paint  would  be  required  to  cover  an 


Relation  of  Covering  to  Space  Inclosed.          367 

oblong  building,  where  the  length  is  twice  the  width,  than 
would  be  required  for  a  circular  one  enclosing  the  same 
floor  space. 

Comparing  the  square  with  the  oblong  building  it  re- 
quires 25  per  cent,  less  wall  to  enclose  it.  From  these  rela- 
tions it  is  clear  that  wherever  it  is  practicable  to  avoid  long 
narrow  buildings  there  will  be  not  only  a  saving  in  mater- 
ials but  the  buildings  may  more  easily  be  kept  warm  in 
winter  and  cool  in  summer,  and  in  the  case  of  silos  there 
will  be  less  loss  of  silage. 


1 

COURT 

WALK 

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STALLS 

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STALLS 
6KIO 

I    STALLS         ~B 

tad  9xi6       10  : 

3X  STALLS 
12 

FEED     PASSAGE         V 

D  HARNESS  C«f 

s  SHOOTS 

M.  HrORAKTS 


NAMES! 

GUTTER 

fr        CUTTER 

S 

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STALLS            I 

5*  xbo        BXIO 

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FEED   PASSAGE 

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(0     12  X  10 

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HA  mas 

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PASSA&E    -,•   • 

FIG.   162. — Showing  the  same  conveniences  in  two  types  of  horse   barns. 

In  Fig.  162  are  represented  two  plans  for  horse  barns 
providing  nearly  identical  accommodations.  The  longer  one 
is  105  feet  10  inches  in  length,  30  feet  wide  with  18  foot 
posts.  The  second  is  75  feet  10  inches  x  44  feet  and  re- 
quires over  8  per  cent,  less  wall  and  over  6  per  cent,  less 
floor  space. 

451.  Relation  of  Hight  to  Capacity — In  the  building  of 
barns,  silos,  ice  houses,  grain  bins  and  root  cellars  the 
more  depth  or  hight  which  can  be  secured  the  larger  will 


368 


'Rural  Architecture. 


be  the  capacity  in  proportion  to  roof,  ceiling  or  floor.  Tlio 
material  for  flooring  and  roofing  a  low  building  is  usually 
no  less  than  is  required  for  a  high  building  and  yet  the 
cubic  contents  are  in  the  ratio  of  their  depth. 

In  the  case  of  hay  barns  and  silos  the  capacities  increase 
much  faster  than  the  hight  because  with  greater  depth  of 
material  it  is  compressed  and  on  this  account  greater  stor- 
age capacity  is  secured. 


Total  Ouhid(   Surfaces.     Excess  of  floor- space 
15  789  SQ  ft  covered  bu  the' 

if   n  *    n        *    '  -*_ 

no  and  Jjarn 


D  ./6048 
B.  Z0210 
C. 


Total  floor-Space 
J\    57365gfl; 
B  66/6  -  *• 
C  11732  -    - 
D 1 3300  -    '' 


JboveB 


96  X  5  A 
20 


40X40 
ZO 


C 


\/8X30 


$0X30 
ZO 


Fro.  163.—  Diagram  showing  the  comparative  outside  snrfnce  and_amonnt  of  floor 
space  in  four  sets  of  barns  represented  in  Figs.  1(51, 105,  Ititi  and  107. 


Relation  of  Covering  to  Space  Inclosed.          369 


FIG.  164.— Cylindrical  barn  \vhicli  accommodates  98  cows  and  10  horses, 
contains  a  granary  and  tool  house,  each  equivalent  to  a  floor  space 
16x40  feet,  aiid  a  400-ton  silo. 


FIG.  165.— Buildings  which  shelter  37  cows  and  15  horses. 


Eural  Architecture. 


452.  Combined  and  Separate  Construction. — The  amount 
of  capital  required  to  build  and  maintain  in  repair  a  large 
number  of  small  buildings  is  greater  than  that  required 
for  a  single  consolidated  structure  providing  like  accommo- 
dations. This  is  clearly  illustrated  by  the  comparative 
chart,  Fig.  163,  which  represents  the  relations  of  build- 
ings shown  in  Figs.  164,  165,  166,  167. 

Taking  the  cylindrical  barn  as  a  standard  of  compari- 
son, it  provides  shelter  for  98  cows  and  10  horses,  contains 
a  400  ton  silo,  a  granary  16x40  feet,  a  tool  space  16x40 
and  storage  capacity  for  all  the  hay  needed;  and  yet  its 
roof  and  side  area  is  only  269  feet  more  than  the  group  of 
buildings  in  Fig.  165,  which  shelters  only  37  cows  and  15 
horses,  has  no  silo,  no  tool  house  and  not  enough  space  for 
hay. 


FIG.  166. — Group  of  buildings  which  shelter  114  cows  and  8  horses. 

Comparing  with  the  buildings  of  Fig.  166,  their  aggre- 
gate outside  surface  exceeds  that  of  the  standard  by  an 


Combined  and  Separate  Construction,  371 

area  64x64  feet  and  yet  they  provide  cramped  quarters  for 
only  114  cows  and  8  horses. 


FIG.  167.— Group  of  buildings  which  shelter  144  cows  and  14  horses  with 
tool  house  and  granary. 

In  the  group  of  buildings  shown  in  Fig.  167,  there  is  an 
aggregate  outside  surface  exceeding  that  of  the  round  barn 
by  140x140  feet,  or  more  than  twice,  and  they  have  less 
floor  space  by  an  area  of  nearly  40x40  feet,  and  the  group 
of  buildings  shelters  but  36  more  cows  and  4  more  horses. 
In  this  last  group  the  buildings  are  both  low  and  narrow, 
causing  extreme  wastefulness  of  lumber. 


FIG.   168.— Consolidated  type   of  barn   showing  driveway   to   second   and 

third  floor. 


372 


Rural  Architecture. 


453.  Saving  of  Labor. — It  is  possible  to  care  for  animals 
•with  less  labor  and  time  where  all  are  brought  together 
under  one  roof  than  it  is  where  they  are  scattered  through 
many  buildings  and  Figs.  164,  168,  169,  170  and^L71  rep- 
resent a  consolidated  type  of  barn  with  composite  func- 
tions, where  all  of  the  stock  are  brought  together  under  one 
roof. 


FIG.  169.— Consolidated  type  of  barn  showing  driveway  to  first  and  second 

floor. 

Economy  in  labor  is  of  much  greater  moment  than 
economy  in  material  because  the  material  simply  repre- 
sents money  invested  in  this  case  while  the  extra  labor  re- 
quired is  a  continual  expense  of  a  high  order. 

454.  Distribution  of  Animals  in  Stables. — The  general 
arrangement  of  animals  in  stables  must  vary  in  detail  in 
almost  endless  variety,  and  individual  circumstances  must 
determine  just  what  is  best.  Three  types  of  arrangement 
for  cows  are  illustrated  in  cross-section  in  Figs.  150  to  159 
under  the  chapter  on  ventilation,  and  Fig.  162  represents 
two  convenient  groupings  for  horses.  While  Fig.  170 
shows  one  plan  of  division  and  arrangement  of  space  in  a 
cylindrical  barn. 


Combined  and  Separate  Construction. 


!73 


?' '  *V^ 

FIG.  170.— Showing  plan  of  the  three  floors  of  Figs.  168  and  169. 


FIQ.  171.— Showing  less  consolidated  type  of  barn  with  silo  partly  outside. 
24 


374 


Rural  Architecture. 


A  combined  cow  and  horse  barn  with  silo  outside  has 
the  arrangement  shown  in  Fig.  172  and  permits  the  work 
being  easily  done. 

455.  Avoiding  the  Use  of  Posts. — In  cow  stables  having  a 
second  story  it  will  often  be  possible  to  carry  the  floor 
upon  the  uprights  used  to  form  the  stalls  or  ties  for  the 
cows  and  in  this  way  save  lumber  by  making  the  same 


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FIG.  172. — Plan  of  combined  cow  and  horse  barn  with  silo  outside. 

pieces  render  double  duty,  and  at  the  same  time  avoid  the 
inconvenience  of  the  posts  and  save  the  space  they  would 
occupy.  This  plan  is  illustrated  in  the  various  figures 
showing  methods  of  ventilation. 


STABLE  FLOCKS. 


456.  Essential  Features — The  essential    features  of  a 
good  stable  floor  are:     (1)  Imperviousness   to  water  and 


'Stable  Floors. 


375 


urine.  (2)  A  surface  sufficiently  even  to  be  readily  and 
thoroughly  cleaned  with  a  small  amount  of  labor.  (3)  A 
durability  approximating  that  of  the  building  itself.  (4) 


FIG.  173. — Rectangular  barn  showing  driveways  to  second  and  third  floors. 

A  reasonably  low  first  cost.  There  are  two  materials 
which  have  been  used  in  the  construction  of  stable  floors 
which  fulfill  these  requirements;  they  are  concretes  made 
either  with  Portland  cement  or  asphalt.  The  asphalt  is 
superior  to  the  Portland  concrete  in  being  a  poorer  con- 
ductor of  heat  while  the  cement  has  the  advantage  of  less 
first  cost. 

457.  Cold  and  Warm  Floors. — It  is  urged  against  the  con- 
crete as  compared  with  wood  floors  that  they  are  cold.  The 
meaning  is  that  they  are  better  conductors  of  heat  and  so 
serve  to  carry  the  heat  away  from  the  body  of  the  animal 
rapidly.  It  is  true  that  they  do  convey  heat  faster  than 
wood  and  when  used  in  cold  climates  without  bedding  are 
worse  than  wood  from  this  standpoint.  They  are  not  as 
bad  in  this  respect,  however,  as  many  imagine.  In  the  first 
place  the  stable  ought  not  to  fall  below  40°  F.,  and  when 


376  Rural  Architecture. 

this  is  true  the  floor  will  only  have  this  temperature  and 
will  not  lead  to  inconvenience  if  other  conditions  are  right. 
In  the  second  place  no  animal  should  be  required  to  lie 


FIG.  174.— Rectangular  barn  with  driveway  to  first  and  third  floors.    Same 

as  Fig.  173. 

even  upon  a  naked  wood  floor  and  when  plenty  of  bedding 
is  provided  the  cement  floor  is  not  too  cold  for  warm  stables 
kept  clean. 

458.  The  Use  of  Bedding. — No  farmer  who  is  attempting 
to  maintain  the  fertility  of  his  land  at  the  standard  of  best 
yield  can  afford  to  use  no  bedding  or  even  a  scanty  supply. 
He  can  better  afford  to  overfeed  with  hay  so  that  the  least 
nutritious  portions  are  rejected  and  use  this  for  bedding, 
than  go  without,  because  the  extra  amount  of  manure  made 
and  the  greater  comfort  and  cleanliness  of  his  animals  will 
pay  a  good  return  for  it.  The  waste  roughage  of  the  farm, 
when  used  as  bedding  and  mixed  with  the  manure,  in- 
creases the  value  of  both  because  it  increases  the  total 
quantity  of  manure  so  much  that  the  fields  can  be  dressed 
more  frequently,  thus  holding  the  humus  content  higher 


Stable  Floors.  377 

and  the  soil  in  better  tilth,  both  essential  conditions  for 
large  yields.  The  liability  of  animals  -to  kick  the  bedding 
off  from  the  floor  is  not  a  sufficient  reason  against  cement 
floors.  It  is  only  when  too  little  bedding  is  used  or  it  has 
not' the  right  texture  that  the  floor  is  left  seriously  exposed. 

459.  All  Wood  Floors. — These  floors  are  generally  laid  in 
one  of  two  ways,  either  close  upon  the  ground,  nailed  to 
stringers  bedded  in  the  earth;  or  else  upon  joists  with  an 
air  space  between  the  floor  and  the  earth.     When  laid  in 
either  of  these  ways  they  are  certain  to  wear  out  through 
the  tramping  of  the  animals  and  'the  use  of  the  tools  in 
cleaning  the  stables,  but  if  conditions  are  favorable  so  that 
rotting  does  not  occur  they  may  last  as  long  as  6  to  12 
years. 

It  is  oftener  true  that  wood  floors  give  out  from  decay 
before  they  do  from  wear.  Where  the  floor  is  kept  con- 
tinually saturated  with,  moisture  it  will  not  decay;  and 
when  kept  continually  dry  it  gives  out  only  through  wear, 
but  when  it  contains  the  right  amount  of  moisture  the 
growth,  of  moulds,  causing  the  decay,  takes  place. 

When  the  floor  is  bedded  in  a  close  textured  clay  soil, 
where  the  subsoil  is  close  and  all  the  time  saturated  with 
water,  decay  will  go  on  very  slowly;  but  where  the  soil  is 
dry  and  open,  and  especially  if  this  is  the  character  of  the 
subsoil,  decay  may  destroy  the  floor  in  3  to  5  years.  So, 
too,  where  the  floors  are  laid  upon  joists  on  the  ground  and 
a  dead  air  space  left,  beneath,  decay  is  certain  to  occur  in 
3  to  5  years,  but  if  the  joists  are  so  arranged  that  there  is 
free  circulation  of  air  beneath,  destruction  from  decay  is 
not  likely  to  occur. 

460.  Making  Wood  Floors  Water  Tight Wood  floors  are 

made  so  as:  to  prevent  water  from  running  through  them 
by  using  more  than  one  layer  with  some  waterproof  com- 
position between  them.     For  heavy  floors  matched  plank 
are  laid  and  coated  with  a  layer  of  coal  tar  roofing  com- 


378  Rural  Architecture. 

position  and  then  upon  this  a  second  layer  of  plank  is  laid, 
painting  the  joints  with  the  same  composition  before 
drawing  them  together.  Lighter  floors  are  made  in  the 
same  way,  using  tongued  and  grooved  flooring. 

461.  Stone  Floors. — Thoroughly  durable  floors  for  cow 
and  horse  stables  are  made  by  bedding  in  clay  rounded 
cobble  stone,  4  or  5  inches  in  diameter,  and  using  upon  this 
an  abundance  of  bedding.       The  uneven  surface  holds  the 
bedding  so  well  that  the  animals  are  fairly  comfortable 
and  neither  wear  nor  decay  will  destroy  them.    The  most 
serious  objection  lies  in  the  difficulty  in  maintaining  clean- 
liness. 

Where  a  good  gutter  is  made  behind  the  cows  and  a  row 
of  cut  stone  10  or  12  inches  wide  are  set  for  the  hind  feet 
to  stand  upon  a  durable  and  quite  satisfactory  floor  is  se- 
cured. 

462.  Macadam  Stable  Floors — A  floor  more  even  in  sur- 
face than  (461)  can  be  made  out  of  carefully  constructed 
macadam  work,  such  as  is  used  in  making  stone  roads, 
giving  it  a  thickness  of  5  or  6  inches.     Where  this  is  used 
there  should  be  provided  cement  gutters  and  mangers  as 
represented  in  Fig.  175. 


FIG.  175.— Shows  method  of  making  a  macadam  stable  floor  with  cement 
mangers  and  gutters. 

Before  laying  such  a  floor  the  ground  should  be  shaped 
and  made  thoroughly  hard  by  tramping  or  ramming.  The 
crushed  stone  should  be  put  on  in  two  layers,  thoroughly 
compacting  the  first  layer  and  filling  the  voids  with  screen- 


Cement  Floors  and  Walks.  379 

ings  before  the  surface  layer  is  made.  Indeed  the  method 
should  be  the  same  as  that  followed  in  making  a  good  stone 
road. 

463.  Macadam  Surface  for  Barnyard — The  paving  or 
flooring  the  barnyard  with  macadam  surface  is  perhaps  the 
best  solution  of  the  difficult  problem  of  maintaining  a  hard 
dry  yard.  On  account  of  the  puddling  of  the  soil  by  the 
tramping  of  feet,  surface  drainage  is  all  thai:  can  be  adopted 
and  hence  even  when  the  yard  has  been  macadamized  it  is 
necessary  to  scrape  the  manure  into  piles  so  that  the  water 
may  flow  away. 


CONSTRUCTION  OF  CEMENT  FLOORS  AND  WALKS. 

464.  Kinds  of  Cement. — There  are  two  classes  of  cement 
on  the  market,  Common  and  Portland.       Of  the  common 
cements  in  the  United  States  familiar  brands  are  Akron, 
Louisville  and  Milwaukee.       They  are  suitable  for  laying 
walls  below  ground  and  plastering  cisterns  but  will  not 
answer  for  stable,  cellar  or  creamery  floors,  nor  for  walks, 
because  they  do  not  make  a  hard  enough  stone. 

For  walks  and  floors  some  brand  of  Portland  cement 
should  be  used.  These  are  American,  English  or  German 
according  to  the  country  in  which  they  are  manufactured. 
American  brands  are  Vulcanite,  Alpha,  Atlas  and  Wol- 
verine. 

465.  Cement  Concrete — The  making  of  cement  concrete 
is  in  effect  the  production  of  artificial  stone  by  binding  to- 
gether pieces  of  rock  and  sand  with  Portland  cement.  The 
cement  is  too  expensive  to  be  used  by  itself  for  ordinary 
work  and  the  making  of  cement  concrete  aims  to  produce 
the  largest  bulk  of  strong  rock  with  the  use  of  the  least  pos- 
sible amount,  of  the  more  costly  cement.     This  is  secured 
when  only  so  much  space  is  left  between  the  materials 
bound  together  as  will  leave  room  for  the  cement  to  form 


380  Rural  Architecture. 

a  thin  laye,r  between  the  faces  of  the  fragments  to  be  joined 
together. 

466.  Materials  for  Concrete  Floors — The  materials  used 
for  cement  walks  and  floors  should  be  (1)  as  large,  clean 
fragments  of  hard  rock  as  can  be  readily  mixed  and  worked 
into  the  forms  and  thickness  of  layer  desired;  (2)  a  finer 
grade  of  crushed  rock  or  coarse  clean  gravel  which  will 
readily  pack  into  the  voids  between  the  larger  fragments ; 
(3)  a  clean,  coarse,  sharp  sand  to  fill  the  pores  between  the 
fragments  of  gravel  or  fine  screenings ;  (4)  enough  Port- 
land cement  to  fill  the  space  between  the  sand  and  bind  the 
whole  together;  (5)  and  finally,  water  enough  to  wet  all 
surfaces,  fill  the  pore  space  of  the  cement  and  make  the 
mortar  plastic. 

467.  Presence  of  Earth,  Loam  or  Dust. — It  is  of  the  great- 
est importance  that  all  of  tli'e  materials  used  be  perfectly 
clean  and  free  from  dirt  or  other  fine  grained  material 
having  the  texture  of  the  cement  itself.       If  a  fine  dust  is 
present  in  the  rock,  gravel  or  sand  it  will  tend  to  form  a 
layer  over  the  surfaces  of  the  fragments  which  prevents 
the  cement  from  coming  in  contact  with  the  pieces  which 
are  to  be  cemented  together  and  a  weak  concrete  results. 
The  fundamental  is  to  have  nothing  but  hard  rock  frag- 
ments large  enough  to  be  cemented  together  and  nothing 
fine  present  but  the  cementing  material  itself. 

In  the  concrete  pavements  used  on  the  streets  of  London, 
and  which  have  a  much  longer  life  than  the  best  paving 
blocks,  great  car"e  is  taken  to  wash  out  of  the  crushed 
granite  and  its  screenings  all  dust  particles  before  using 
them,  although  the  dust  may  be  from  the  granite  itself. 

468.  Wetting  the  Crushed  Rock  Before  Use. — There  are 
two  important  reasons  why  crushed  rock  or  coarse  screened 
gravel,  to  be  used  as  the  body  of  concrete,  should  be  wet  be- 
fore mixing  with  the  cement.     These  are  (1)  to  displnco 
as  much  adhering  air  as  possible,  and  (2)  so  as  not  to  draw 


Cement  Floors  and  Walks.  381- 

out  from  the  cement  the  water  needed  to  maintain  its 
plasticity  and  to  assist  in  the  setting. 

If  the  coarse  materials  are  mixed  with  the  cement  dry 
a  large  amount  of  air  will  be  set  free  and  entangled  in  the 
concrete,  which  will  prevent  all  spaces  being  filled,  but  the 
chief  difficulty  conies  from  the  air  preventing  the  cement 
from  adhering  to  the  surfaces.  So  strongly  does  air  adhere 
to  coarse  sand  that  it  must  be  boiled  some  time  under  water 
before  it  is  all  removed. 

469.  Ratio  of  Ingredients  for  Concrete. — The  amounts  of 
each  ingredient  required  to  make  a  solid  concrete  with  all 
spaces  filled  depends  upon  the  pore  space  in  the  different 
materials.    Trautwine  assumes  that  for  each  ingredient  the 
voids  are  near  enough  to  50  per  cent,  so  that  as  a  safe  work- 
ing basis  this  should  be  taken. 

To  make  a  cubic  yard  of  concrete  it  would  be  necessary 
to  use,  on  Trautwine's  basis, 

Crushed  rock.  Gravel  or  screenings.  Coarse  sand.  Cement. 

27  cu.  ft.  13.5  cu.  ft.  6.75  cu.  ft.  3.375  cu.  ft . 

This  ratio  for  pore  space  is  certainly  larger  than  is  likely 
to  occur  and  for  farm  purposes  it  will  be  safe  enough  to 
take  the  ratios  of 

Crushed  rock.  Gravel  or  screenings.  Sand.  Cement. 

27  cu.  ft.  12.69  cu.  ft.  5. 584  cu  ft.  2. 122  cu.  ft. 

These  figures  assume  the  pore  space  of  the  rock  to  be  47 
per  cent.,  of  the  gravel  44  per  cent,  and  of  the  sand  38  per 
cent. 

470.  Ratio  of  Ingredients  for  Finishing. — Where  good 
plastering  sand  is  used  for  making  the  finishing  surface  the 
pore  space  to  be  filled  will  be  about  35  per  cent,  and  this 
would  require  a  little  more  than  one  of  cement  to    two    of 
sand,  and  unless  there  is  some  gravel  or  screenings  to  use 
with  the  sand  it  will  be  safer  to  make  the  facing  2  of  sand 
to  1  of  cement. 


382 


Rural  Architecture. 


471.  Thickness  of  Floor. — For  most  stables  where  the 
ground  has  been  well  firmed  and  shaped  a  thickness  of  4 
inches  of  concrete  and  one-half  inch  of  facing  will  be 
enough;  for  house  cellars  and  for  the  bottoms  of  silos  3 
inches  of  concrete  and  one-fourth  inch  of  facing  will  do. 
For  creameries  and  milk  rooms  the  concrete  better  be  4 
inches  and  the  facing  a  full  half  inch,  made  richer  in  ce- 
ment, in  the  ratio  of  one  to  one. 

472.  Making  the  Concrete — The  cement,  sand  and  gravel 
are  put  together  dry  on  a  mixing  board  and  thoroughly 
worked  over,  then  enough  water  added  to  make  a  stiff  paste. 
The  right  amount  of  crushed  rock  is  thoroughly  drenched 
with  water  and  the  whole  mixed  by  shoveling  until  the 
rock  is  thoroughly  incorporated  with  the  cement. 

473.  laying  the  Concrete. — The  floor  of  the  stable  should 
first  be  given  the  proper  form  and  very  thoroughly  tamped 
so  that  no  settling  shall  occur  after  the  floor  is  laid.     The 
concrete  should  be  laid  in  blocks  four  or  five  feet  square, 
building  alternate  blocks  first,  Fig.  1Y6,  so  as  to  give  time 


-.."-r^_-      ^—y*~*:~  _; " _,--_     ..-.rc\' 


FIG.   176.— Shows   method   of   laying   cement   floors   in   blocks  to   prevent 

cracking. 

for  setting  and  prevent  a  strong  union  of  the  blocks.  If 
the  floor  is  not  laid  in  this  manner  shrinkage  cracks  will 
occur.  The  concrete  should  be  made  only  as  fast  as  used 


Cement  Floors  and  Walks.  383 

and  should  be  thoroughly  rammed  until  the  fine  cement 
shows  as  a  layer  on  the  surface.  After  standing  a  short 
time,  but  before  the  concrete  has  set,  the  finisliing  surface 
should  be  applied  and  thoroughly  troweled  until  it  is  even 
and  smooth.  Fig.  1Y7  is-  a  cross  section  of  floor  and 
mangers. 


FIG.  177. — Shows  cross-section   of  cement   stable   floor   with   mangers   and 

gutters. 


For  a  cellar  or  creamery  floor,  where  it  is  desired  to  have 
a  fine  smooth  surface,  easily  cleaned,  after  troweling,  it 
may  be  wet  with  a  whitewash  brush  and  some  pure  dry  ce- 
ment sprinkled  over,  which  is  troweled  until  it  is  hard, 
smooth  and  glossy. 

When  the  second  series  of  blocks  in  a  given,  tier  is  made 
and  the  surface  finished  it  is  necessary  to  cut  through  the 
finishing  layer  exactly  above  the  joint  in  the  concrete,  to 
prevent  cracking,  and  then  neatly  round  the  joint. 

474.  Cost  of  Materials  for  Cement  Floor. — Taking  mater- 
ials at  the  prices  given  and  the  concrete  4  inches  thick, 
made  in  the  proportions  of  (469)  the  cost  per  100  square 
feet  of  floor,  and  the  amount  of  materials  will  be  as  given 
in  the  table  below : 

The  floor  made  of  wood  2  inches  thick,  laid  upon  2x6's, 
16  inches  from  center  to  center,  would  cost  $4.12  or  $4.95 
per  100  square  feet  when  the  price  is  $15  or  $18  per  thou- 
sand. This  makes  the  concrete  99  cents  per  100  square 
feet  more  than  the  lumber,  comparing  the  lowest  prices  in 
each  case,  and  $1.72  more,  comparing  the  higher  prices. 


384 


Rural  Architecture. 


Material  required  for  100  square  feet  of  concrete  floor  4  inches 
thick  with  one -half  inch  of  facing. 


Material. 

Amount. 

Cost  per  100  sq.  ft. 

1  23  cu.  yds 

$    80  per  cu.  yd    $    9S4 

Sand  and  gravel  
Cement  

.73  cu.  yds  
3.76  cwt  

.50  per  cu.  yd.       .365 
1.00  per  cwt.         3.760 

Total    5.109 

Crushed  rock  
Sand  and  gravel  

1.23cu.  yds  
.73  cu.  yds  
3.76  cwt  .     . 

1.00  percu.  yd.     1.23 
.75  per  cu.  yd.       .55 
1  30  per  cwt.         4  89 

Total  

$6.67 

Where  crushed  rock  cannot  be  had,  but  coarse  gravel  and 
plastering  sand  are  available,  a  good  floor  can  be  made,  but 
more  cement  must  be  used,  usually  4  of  sand  and  gravel  to 
1  of  cement. 


TIES   FOE   CATTLE. 

The  methods  of  tying  cattle  must  vary  widely  with  the 
taste  and  objects  of  the  owner.  The  essential  objects  to  be 
secured  are:  (1)  comfort  for  the  animals.  This  is  neces- 
sary whether  the  main  object  is  milk,  breeding  or  beef ;  (2) 
cleanliness,  and  (3)  economy  of  time  in  tying  and  of  space. 

3E 


FIG.  17&— Wilder  swinging  stanchion. 


FIG.  179.— Scott  self-closing  swinging 
stanchion. 


475.  The  Stanchion. — There  is  no  tie  for  cows,  if  we  ex- 
cept -the  plain  halter  or  rope,  which  has  been  so  universally 


Ties  for  Cattle. 


385 


used  as  one  of  the  forms  of  stanchions  represented  in  Figs. 
178,  179  and  186.  It  is  the  simplest,  cheapest  and  most 
expeditious  tie  invented  and  the  swinging  forms  which  per- 
mit the  yoke  to  turn  and  to  move  a  little  back  and  forth 
provide  a  reasonable  amount  of  comfort;  and  where  the 
width  of  the  platform  is  adapted  to  the  size  of  the  animal 
they  secure  as  high  a  degree  of  cleanliness  as  is  practicable. 


FIG.  180.— Thorp  stall. 


FIG.  181.— Drown  stall. 


476.  Adjustable  Stalls. — The  four  stalls  represented  in 
Figs.  180,  181,  182,  and  183  are  designed  to  give  the  cows 
the  maximum  amount  of  freedom  of  head  movement  but  to 
force  them  to  stand  close  enough  to  the  gutter  to  prevent 
the  platform  being  soiled.  The  manger  or  the  head  of  the 
stall  is  made  adjustable  so  as  to  crowd  the  cow  back  against 
the  chain  in  the  rear  which  confines  her.  Practically  there 
is  no  form  of  tie  which  can  prevent  the  cow  from  soiling 
the  platform  upon  which  she  stands  on  account  of  the  un- 
changable  habit  of  shortening  the  body  by  humping  the 
back  when  the  evacuations  occur. 


FIG.  182.— Roberts  stall. 


FIG.  183.— Bidwell  stall. 


386 


Rural  Architecture. 


The  two  stalls,  Figs.  184,  185,  have  been  designed  to  se- 
cure cleanliness  in  spite  of  this  habit.  In  the  Newton  tie 
it  is  expected  that  while  the  cow  is  standing  the  yoke  to 
which  she  is  tied  will  force  her  back  sufficiently  to  prevent 
the  difficulty.  In  practice,  however,  there  is  necessarily  so 


FIG.  184.— Knapp  tie 


FIG.  185.— Newton  tie. 


much  freedom  at  the  neck  that  the  object  is  not  secured. 
The  "Model  tie"  provides  a  bar  on  the  floor,  just  in  front  of 
where  the  cow's  feet  are  forced  to  be  while  standing  and 
feeding,  and  which  is  so  much  of  an  obstruction  that  in 
order  to  lie  in  comfort  she  steps  forward  enough  to  He  on 
the  clean  bedding. 


Fig.  186.— Rigid  stanchion. 


FIG.  187.— "Model  tie. 


Ties  for  Cattle. 


387 


477.  Movable  Halter  Ties — Another  class  of  ties  repre- 
sented in  Figs.  188,  189,  attempt  to  confine  the  cow  in 
movements  forward  and  backward  by  using  a  short  chain 
which  slides  at  the  other  end  in  such  a  manner  as  to  per- 
mit freedom  of  motion  up  and  down. 


FIG.  133.—  Chain  tie. 


Fid.  189.— Baker  tie. 


478.  Tight  Side  Partitions. — There  is  an  effort  among 
some  feeders  to  prevent  the  animal  from  moving  sidewise 
so  as  to  interfere  with  the  neighbor,  either  by  stepping 
upon  the  feet  or  teats  of  the  cow  lying  down  or  of  taking  the 
food  from  the  manger.    Where  such  provisions  are  insisted 
upon  it  should  be  kept  in  mind  that  anything  which  tends 
to  enclose  the  cow,  especially  her  head,  in  a  tight  box  tends 
in  a  high  degree  to  defeat  the  purposes  of  good  ventilation 
by  confining  the  air  once  breathed  about  the  animal,  hence 
such  arrangements  should  be  slatted  or  else  open  at  the  level 
of  the  floor. 

So,  too,  wherever  box  stalls  are  used  these  should  be 
slatted  or  open  at  the  bottom  and  not  "boxes"  as  they  too 
often  are. 

479.  Tying  for  Feeding  Only — For  calves,  young  cattle 
and  feeding  steers  there  is  perhaps  no  mode  of  confining 
the  animals  in  the  stable  so  good  as  to  give  them  complete 
freedom  except  at  the  time  of  feeding,  using  plenty  of  bed- 
ding on  a  cement  floor  which  is  cleaned  as  often  as  needful. 


388  Rural  Architecture. 

In  such  cases  the  stanchion  'tie  is  the  best  as  everything  is 
then  reduced  to  the  simplest  conditions. 

480.  Mangers. — One  of  the  simplest  mangers  for  feeding 
cows  is  represented  in  Fig.  177,  and  when  made  of  cement 
as  represented  in  the  cut  it  is  the  best  for  feeding,  cleaning 
and  watering,  where  large  numbers  of  animals  are  to  be 
handled  with  the  greatest  economy.     The  manger  should 
have  an  inside  width  of  at  least  2  feet,  a  depth  of  8  inches 
and  should  have  its  bottom  3  or  4  inches  above  the  plat- 
form upon  which  the  cows  stand. 

481.  The  Manure  Drop. — This  should  have  a  width  for 
adult  cows  not  less  than  18  inches  and  not  more  than  20 
inches.    Its  depth  next  to  the  animals  may  be  8  inches  and 
on  the  rear  side  6  inches.     These  dimensions  give  ample 
capacity  to  prevent  the  walk  behind  from  being  soiled  and 
make  it  easily  cleaned. 

On  some  accounts  a  depth  of  6  inches  next  to  the  cows 
and  6  inches  in  the  rear  is  best;  and  where  a  wagon  is 
driven  behind  "the  animals  to  clean  the  stable  a  depth  be- 
hind of  only  4  inches  gives  less  hight  to  lift  the  manure. 


PEOVISIONS  FOK  WATERING. 

Where  there  is  a  well  of  ample  capacity,  and  30  or  more 
cows  are  kept,  the  best  arrangement,  everything  considered 
is  to  pump  the  water  from  the  well  at  the  time  it  is  needed. 
This  plan  provides  water  that  is  both  fresh  and  natural 
temperature,  and  does  away  with  expensive  storage  tanks. 
In  case  the  power  is  pumping  waiter  faster  than  is  needed 
it  is  a  simple  matter  to  provide  an  overflow,  returning  the 
water  to  the  well. 

482.  Watering  in  the  Barn. — In  climates  having  severe 
winters  it  is  best,  if  practicable,  to  water  the  animals  in 
the  barn,  and  where  a  good  fresh  running  stream  can  be 


Provisions  for  Watering. 


389 


maintained  the  ideal  way  is  to  have  the  water  before  the 
cows  all  the  time  so  that  it  can  be  taken  when  desired. 

It  is  not  desirable  to  keep  water  standing  before  the  cows 
continuously  as  it  is  certain  to  become  foul ;  but  it  may  be 
maintained  during  the  greater  part  of  the  day  if  the  drink- 
ing basins  or  troughs  are  emptied  clean  each  evening. 

483.  Methods  of  Watering  in  the  Stable. — We  have  seen 
but  two  reasonably  satisfactory  methods  of  watering  a  large 
number  of  cattle  in  the  stable,  and  these  are  either  to  clean 
the  manger  and  run  the  water  into  that  or  else  to  have  a 
special  long  watering  trough  used  for  that  alone. 


FIG.  190.— Simple  arraiigement  for  watering  cows  in  stable. 


The  simplest  arrangement  of  special  trough  is  repre- 
sented in  Fig.  190,  and  extends  the  full  length  of  the  stable, 
the  water  coming  to  it  from  above  so  that  the  supply  pipe 
is  entirely  above  ground  where  it  can  be  gotten  at  and  can 
be  emptied  at  once  after  using.  The  trough  is  covered  its 
entire  length  with  a  hinged  lid,  but  in  front  of  each  cow  the 
lid  is  cut  so  the  cow  can  raise  a  section  with  her  nose  when 
drinking,  letting  it  fall  when  she  is  through. 

484.  Storing  Water  in  Tanks — Where  there  is  a  basement 
barn  the  best  arrangement  for  a  storage  water  tank  is  a 
25 


390 


Rural  Architecture. 


cement  lined  cistern  beneath  the  surface  in  the  hill  above 
the  barn.  Such  a  cistern  is  less  expensive,  is  a  permanent 
improvement  and  will  keep  the  water  warm  and  clean. 

We  have  seen  cases  where  a  satisfactory  cement  lined 
cistern  is  built  entirely  above  ground  and  then  covered  in 
by  grading  a  mound  of  earth  about  and  over  it  sufficient  to 
make  it  frost  proof.  Such  a  cistern  should  be  provided 
with  a  man-hole  so  that  it  may  be  entered  if  necessary. 

485.  Watering  Trough. — Where  stock  is  watered  in  the 
yard  a  good  arrangement  for  winter,  where  the  ground  is 
porous,  is  represented  in  Fig.  191.  The  tank  is  a  galvan- 
ized cylinder  3  or  more  feet  in  diameter  and  5  feet  deep 
•which  stands  in  a  dry  well  15  or  more  feet  deep  and  so  ar- 
ranged that  the  warm  air  from  the  bottom  of  the  well  all 
the  time  surrounds  the  tank  and  keeps  it  from  freezing. 
Water  may  be  pumped  into  this  direct  or  it  may  be  sup- 
plied from  the  bank  cistern.  When  it  is  necessary  to 
empty  the  tank  the  plug  can  be  removed  and  the  water  al- 
lowed to  drain  into  the  dry  well. 


FIG.  191.— Representing  a  storage  reservoir  and  drinking  tank  arranged  to 
avoid   freezing. 

It  is  of  course  important  to  provide  a  warm  jacket  about 
the  tank  and  cover,  as  represented,  so  as  to  assist  in  keeping 
the  water  warm. 


Arrangements  for  Unloading  Hay. 


391 


ARRANGEMENTS  FOR  UNLOADING   HAY. 

486.  Unloading  Direct  from  Wagon. — Where  the  hay  is 
not  to  be  lifted  and  can  be  rolled  directly  from  the  wagon 
with  the  fork  into  the  bay,  there  is  no  simpler  and  more  ex- 
peditious way ;  and  where  the  load  can  be  driven  to  the  top 
of  the  barn,  as  represented  in  Figs.  168,  171  and  173,  there 
is  little  need  of  other  mechanical  arrangements. 


Fio.   192.— Curved   track  and   hay   carrier  for   use  in    cylindrical   barn. 

487.  Unloading  Hay  in  Cylindrical  Barns. — Where  the 
cylindrical  type  of  barn  is  used  there  are  two  methods  of 
distributing  the  hay;   (1)  that  represented  in  Fig.  192, 
where  an  ordinary  hay  carrier  is  moved  over  a  curved  track 
and  (2)  that  represented  in  Fig.  193,  where  an  ordinary 
hay  carrier  delivers  the  hay  upon  a  central  inclined  plat- 
form, which  is  turned  about  by  the  operator  in  the  bay  so 
as  to  deliver  the  hay  at  any  desired  point. 

488.  Tilting  Hay  Distributor. — It  is  possible  to  take  ad- 
vantage of  the  principle  illustrated  in  Fig.  193  for  distrib- 


392 


Rural  Architecture* 


FIG.   193.— Ordinary    hay    r-nrrier  nn<l    revolving   platform   for   distributing 
hay  in  cylindrical  barn. 


FIG.  104.— Representing  a  movable,  tilting  platform  for  distributing  haj 
in  rectangular  barn. 


Arrangements  for  Unloading  Hay.  393 

uting  hay  in  ordinary  rectangular  barns,  whose  timbers  are 
not  in  the  way.  Fig.  194  represents  a  tilting  platform, 
which  rocks  upon  two  bars  carried  by  four  cables  secured 
to  pulleys  which  roll  along  tracks  or  cables  secured  to 
rafters,  as  shown  in  the  cut.  With  this  arrangement  hay 
may  be  dropped  at  either  side  or  in  the  center  of  the  bay, 
as  desired. 


CHAPTEK  XIX. 

CONSTRUCTION  OF  SILOS. 

489.  Conditions   Essential   for   Preserving   Silage The 

only  conditions  necessary  for  preserving  good  corn  and 
clover  silage,  are  close  packing  in  an  air  tight  structure 
when  the  materials  have  reached  the  right  stage  of  matur- 
ity.    Whatever  means  may  be  adopted  to  exclude  air  from 
these  materials  will  preserve  them  as  silage.     If  air  can 
find  access  to  it  spoiling  will  be  inevitable  and  the  rate  and 
extent  will  be  greater  the  more  readily  air  can  gain  access. 

490.  Depth  of  Silage.— The  depth  of  silage  should  be 
made  as  great  as  practicable  (1)  because  in  this  way  the 
largest  amount  of  feed  per  cubic  foot  may  be  stored.      (2) 
There  is  less  loss  relatively  at  the  surface.     (3)  The  strong 
lateral  pressure  forces   the   silage   against  the  walls   so 
closely  that  less  air  enters  and  hence  there  is  less  loss. 

491.  Silo  Walls  Must  be  Rigid  and  Strong — The  outward 
pressure  of  cut  corn  silage  when  settling,  at  the  time  of 
filling,  increases  with  the  depth  at  the  rate  of  11  Ibs.  per 
square  feet  for  each  foot  of  depth.     At  a  depth  of  10  feet 
the  lateral  pressure  is  110  Ibs.  per  square  foot,  at  20  feet  it 
is  220  Ibs.  and  at  30  feet  330  Ibs. 

Because  of  this  great  pressure  silo  walls  must  be  made 
very  strong  when  they  have  a  depth  of  20  or  more  feet.  It 
is  difficult  to  make  deep  rectangular  silos  whose  walls  will 
not  spread  as  represented  in  Fig.  195,  and  where  this  takes 
place  the  walls  are  crowded  away  from  the  silage  so  much 
that  air  can  circulate  up  and  down  next  to  the  walls  and 
this  results  in  heavy  losses. 


Essential  Features  of  Silos. 


395 


In  circular' silos  the  pressure  is  sustained  by  the  tensile 
strength  of  the  materials  in  the  walls,  which  gives  them  the 
greatest  possible  advantage. 


FIG  195.— Illustrating  how  the  bulging  of  rectangular  wooden  silo  walls 
allows  air  to  come  down  the  sides  between  the  walls  and  the  silage, 
causing  it  to  spoil.  The  amount  of  spreading  is  exaggerated  in  the 
figure  for  clearness  of  illustration,  but  it  is  none  the  less  real. 

492.  Silo  Placed  Deeply  in  the  Ground. — In  most  cases  it 
is  best  to  allow  the  silo  to  extend  as  deeply  into  the  ground 
as  convenience  in  removing  the  materials  will  permit.  This 
can  always  be  as  much  as  3  feet  below  the  feeding  floor  and 
in  the  case  of  bank  barns  where  the  silo  can  be  placed  in  the 


Rural  Architecture. 


hill  a  depth,  of  11  or  more  feet  can  easily  be  secured. 
Placing  the  silo  deep  saves  elevating  the  silage  so  high 
when  filling  and  a  large  portion  of  it  is  below  frost. 


FIG.  196. — Showing  an  all-stone  silo  with  conical  roof  and  openings  for 
feeding  doors;  the  heavy  black  clots  1,  1,  1  show  where  Iron  rods  may 
be  bedded  in  the  wall  to  prevent  cracking  from  the  pressure  of  the 
silage.  Method  of  constructing  silo  door  and  door  jamb  for  stone 
silo.  K  shows  cross  section  of  silo  door,  P  shows  how  the  door 
jam6  is  made  to  make  it  air  tight,  and  how  the  door  is  held  in  place 
with  lag  bolts  against  a  gasket  of  ruberoid  roofing. 

493.  Protection  Against  Frost. — It  is  not  necessary  to 
build  a  silo  so  as  to  be  entirely  frost  proof  in  cold  climates, 
but  it  will  pay  to  build  them  reasonably  warm  where  they 
are  to  be  fed  from  during  cold  weather.  The  freezing  of 
silage  does  not  injure  it  seriously  but  it  is  not  well  to  feed 
it  when  frozen.  If  a  silo  is  not  to  be  opened  until  warm 
weather  no  special  attention  need  be  given  to  warmth.  If 
a  silo  is  10  to  13  feet  in  the  ground  and  only  20  feet  above 


Construction  of  Stone  Silos.  397 

ground,  the  settling  and  the  early  feeding  before  severe 
cold  weather  will  usually  have  carried  the  surface  of  tho 
silage  so  low  that  little  inconvenience  from  frost  will  be 
experienced  even  in  stone  silos.  In  all  the  wooden  silos,  ex- 
cept the  questionable  stave  types,  the  construction  needed 
for  strength  and  to  keep  the  air  from  the  silage  will  usually 
be  a  sufficient  protection  against  frost. 


CONSTEUCTION  OF  STONE  SILOS. 

Whenever  stone  can  be  had  on  the  farm  suitable  for 
building  purposes  these  may  be  used  in  silo  construction, 
thus  converting  idle  into  active  capital.  So  far  as  the  silo 
itself  is  concerned  no  better  or  more  durable  material  can 
be  used,  and  where  it  can  be  10  to  13  feet  in  the  ground 
the  inconveniences  from  freezing  will  be  small,  and  the 
stone  silo  will  be  found  one  of  the  cheapest  of  the  thor- 
oughly good  forms.  Great  pains  should  be  taken  in  build- 
ing the  walls  to  fill  all  spaces  between  stones  solid  with 
smaller  ones  and  mortar  and  to  have  them  thoroughly 
bonded  in  order  to  secure  strength  and  prevent  cracking. 

494.  Laying  the  Wall — The  portion  of  the  silo  wall 
which  is  below  ground  better  be  about  2  feet  thick  and  laid 
in  one  of  the  cheap  brands  of  cement  rather  than  lime,  the 
cement  being  desirable  because  lime  mortar  becomes  hard 
so  very  slowly  in  heavy  walls,  especially  below  ground. 
After  the  wall  is  two  feet  above  ground  good  lime  mortar 
may  be  used,  but  in  this  case  there  ought  to  be  at  least  two 
months  for  the  wall  to  season  and  set  before  filling.  The 
upper  portion  of  the  silo  wall  need  not  be  heavier  than  18 
inches,  and  if  the  size  of  stone  permit  of  it,  the  outer  face 
of  the  wall  may  be  drawn  in  gradually  to  a  thickness  of  12 
inches  at  the  top. 

Too  great  care  cannot  be  taken  in  making  the  part  of  the 
wall  below  and  near  the  ground  solid,  and  especially  its 
outer  face,  so  that  it  will  be  strong  where  the  greatest  strain 


39,8  . 


Rural  Architecture. 


will  come.    It  is  best  also  to  dig  the-  pit  for  the  silo  large 
enough  so  as  to  have  plenty  of  room  outside  of  the  finished 

wall  to  permit  the  earth 
filled  in  behind  to  be  very 
thoroughly  tamped  so  as 
to  act  as  a  strong  backing 
for  the  wall.  This  is 
urged  because  a  large  per 
cent,  of  the  stone  founda- 
tions of  wood  silos  have 
cracked  more  or  less  from 
one  cause  or  another  and 
these  cracks  lead  to  the 
spoiling  of  silage. 

Flat  quarry  rock,  like 
limestone,  will  make  the 
strongest  silo  wall,  be- 
cause they  bond  much 
better  than  boulders  do, 
and  when  built  of  lime- 
stone they  will  not  need 
to  be  reinforced  much 
with  iron  rods.  It  will  be 

FIG.  197— Shows  the  method  of,  jacketing  a  kest     even     in     this     Case, 
stone  silo  to  protect  it  against  frost ;  the  . 

heavy  black  squares  are  blocks  bedded  into  however,    tO    US6   the    iron 
the  stone  wall  to  which  girts  or  studs  may    .  ,     ,  ,      -. 

be  nailed  to  carry  the  siding.  tie  rods  between  the  lower 

two  doors. 


495.  Plastering — The  inner  face  of  the  silo  wall  should 
be  plastered  with  a  thin  coat  of  rich  cement  not  leaner  than 
1  of  cement  to  1.5  or  2  of  clean  sharp  sand.  If  the  mortar 
is  not  rich  and  troweled  smooth,  the  acids  of  the  silage  will 
act  upon  it  much  more  rapidly,  dissolving  out  the  lime  and 
leaving  it  open  and  porous. 

It  will  usually  be  prudent  also  to  whitewash  these  linings 
every  two  or  three  years,  especially  the  lower  portion  where 
the  silage  is  longest  in  contact  with  the  cement,  in  order  to 
prevent  softening,  using  cement  to  make  the  whitewash. 


Construction  of  Stone  Silos. 


399 


496.  Doors.— Doors  for  filling  and  feeding  should  be  ar- 
ranged as  represented  in  A,  Fig.  196,  and  if  the  lower  one 
is  long,  cutting  out  a  good  deal  of  the  wall,  an  iron  rod 
should  be  bedded  in  the  wall  above  it  to  prevent  cracking 
between  the  doors.  The  rod  should  be  of  f  inch  round  iron 
bent  to  the  curve  of  the  circle  and  about  12  feet  long.  The 
two  ends  should  be  turned  short  at  right  angles,  so  as  to 
anchor  better  in  the  mortar. 

In  deep  stone  silos,  which  rise  more  than  18  feet  above 
the  surface  of  the  ground,  it  will  be  safest  to  strengthen  the 
wall  between  the  two  lower  doors  with  iron  tie  rods  and,  if 
such  a  silo  is  built  of  boulders,  it  will  be  well  to  use  rods 
enough  to  make  a  complete  line  or  hoop  around  the  silo 
about  two  feet  above  the  ground,  as  represented  in  Fig. 
198. 


FIG.  198.— Showing  method  of  bedding  iron  rods  in  stone,  brick  or  con- 
crete silo  walls  to  increase  the  strength.  The  heavy  lines  with  ends 
bent  represent  the  iron  rods. 

The  door  jambs  for  the  stone  silo  are  best  made  of  4x4's 
framed  together  and  set  far  enough  apart  to  give  a  depth 
four  inches  less  than  the  thickness  of  the  wall.  This  will 
allow  mortar  to  be  filled  in  between  the  4x4's  to  make  an 


400  Mural  Architecture* 

air-tight  joint.  A  6-inch  board  may  be  fitted  around  the 
outside  of  the  inner  side  of  the  door  jambs  to  form  the  rab- 
bet for  the  doors,  or  the  jambs  may  be  made  as  represented 
in  Fig.  196.  There  will  be  slight  shoulders  left  in  the 
round  stone  silo  above  and  below  the  doors  when  these  are 
made  flat,  and  these  should  be  filled  out  with  mortar  when 
plastering,  giving  a  long,  gentle  slope  back  to  the  wall. 

The  door  is  best  made  of  two  layers  of  6-inch  flooring, 
tongued  and  grooved,  crossing  at  right  angles,  nailed  or 
screwed  together,  with  a  layer  of  good  acid  and  water 
proof  paper  between,  as  shown  at  E,  Fig.  196.  To  make 
the  door  fit  perfectly  air-tight  there  should  be  tacked  to  the 
face  of  the  door  jamb,  all  around,  a  wide  strip  of  thick  roof 
paper  or  strips  of  old  worn  out  rubber  belting,  and  the  door 
drawn  up  against  this  with  four  £x4  inch  lag  bolts  pro- 
vided with  washers. 

If  one  prefers  to  do  so  the  door  may  be  made  small 
enough  so  as  to  leave  a  half-inch  space  between  it  and  the 
jamb  all  around,  and  this  space  filled  with  puddled  clay 
after  the  door  is  put  in  place.  Either  of  these  methods  is 
better  than  to  tack  strips  of  tar  paper  over  the  joints. 


CONSTRUCTION   OF  BKICK  SILOS. 

Very  excellent  silos  may  be  made  of  brick,  as  repre- 
sented in  Fig.  199,  and  where  brick  of  a  good  quality  can 
be  obtained  at  $4.25  to  $7.00  per  thousand  a  silo  which  will 
last  indefinitely  may  be  made  at  a  moderate  cost. 

497.  Foundation — The  foundation  of  the  brick  silo  is 
best  made  of  stone,  wherever  these  may  be  had,  carrying 
the  stone  work  up  at  least  a  foot  above  the  ground  and  be- 
ginning below  frost  line.  The  brick  work  will  then  be  set 
with  its  inner  face  flush  with  the  inner  surface  of  the  stone 
work. 

If  the  silo  is  to  be  carried  20  or  more  feet  above  the  stone 
wall  it  will  be  desirable  to  bed  a  |-inch  round  iron  hoop 


Construction  of  Brick  Silos. 


401 


into  the  upper  surface  of  the  stone  work  in  order  to  guard 
against  cracking  the  wall  by  the  pressure  of  the  first  filling 
before  the  mortar  has  had  time  to  thoroughly  season,  which 


FIG.  199.— Shows  an  all-brick  silo  with  wall  14  inches  thick  made  of  three 
courses  of  brick,  the  outer  course  being  set  so  as  to  form  a  2-inch 
dead  air  space  as  high  up  as  the  shoulder. 

does  not  take  place  until  after  five  or  more  months.  The 
method  of  laying  the  sections  of  iron  rod  in  the  wall  is  rep- 
resented in  Fig.  198. 


402  Rural  Architecture. 

498.  Walls. — In  cold  climates  it  will  be  best  to  make  the 
lower  portion  of  the  wall,  up  to  within  10  feet  of  the  top, 
with  a  2-inch  dead  air  space,  using  three  courses  of  brick, 
thus  making  the  wall  14  inches  thick,  for  all  the  smaller 
and  medium  sized  silos.       If  the  silo  is  to  exceed  24  feet 
inside  diameter  the  lower  third  of  the  brick   wall   should 
be  made  of  four  courses  of  brick  and  18  inches  thick, 
the  second  third  14  inches  thick,  and  the  upper  third  8 
inches,  solid.       The  dead  air  space  should  be  next  to  the 
outside  and  this  course  of  brick  should  be  tied  to  the  inner 
wall  as  frequently  as  necessary  to  make  k  stable. 

499.  Strengthening  the  Walls. — The    tendency    of    the 
pressure  of  the  silage  to  crack  the  walls  of  round  silos  in- 
creases with  the  depth  and  with  the  diameter  of  the  silo. 
The  tendency  of  the  silage  to  burst  a  silo  26  feet  inside 
diameter  is  twice  as  great  as  in  one  13  feet  in  diameter  and 
the  same  depth,  and  this  makes  it  necessary  to  strengthen 
the  walls  of  the  larger  brick  silos.     In  all  brick  silos  there 
should  be  an  iron  tie  rod  bedded  in  the  wall,  in  the  manner 
illustrated  in  Fig.  198,  between  each  of  the  lower  doors  to 
compensate  for  the  weakening  caused  by  the  doors;  and  in 
the  larger  silos  these  ties  should  extend  entirely  around  the 
silo  in  the  manner  shown  in  Fig.  198. 

500.  Wetting  Brick. — It  is  very  important  in  laying  the 
brick  for  a  silo  wall  that  they  should  be  wet  and  especially 
if  the  work  is  done  in  hot,  dry  weather.    If  this  is  not  done 
the  brick  will  so  completely  dry  out  the  mortar  that  it  can- 
not set  properly  and  become  strong. 

501.  Making  Walls  Air  Tight. — There  are  several  ways 
in  which  this  may  be  done,  and  some  of  these  will  be  given 
in  the  reverse  order  of  their  effectiveness. 

1.  After  the  wall  is  finished  it  may  be  simply  given  two 
coats  of  thick  cement  whitewash,  and  this  repeated  every 
two  or  three  years  as  the  acid  of  the  silage  dissolves  it  away. 

2.  The  face  of  the  brick  wall  may  be  given  a  good,  rich 


Construction  of  Brick-lined  Silos.  403 

coat  of  cement  plaster,  one-fourth  to  one-half  an  inch  thick, 
and  then  this  be  kept  whitewashed  so  as  to  neutralize  the 
acid  and  prevent  it  from  softening  the  cement. 

3.  The  wall,  or  at  least  the  inner  portion,  may  be  laid  in 
rich  cement  mortar, making  the  horizontal  joints  about  one- 
fourth  of  an  inch  thick  and  the  vertical  ones  a  half  inch 
thick,  taking  great  care  to  get  all  joints  of  the  inner  tier  of 
brick  thoroughly  filled  with  mortar.       This  method  will 
place  the  cement  where  it  will  not  be  as  readily  affected  by 
the  acids  and  frost  and  does  away  with  the  necessity  of 
plastering,  care  being  taken  to  lay  the  brick  smoothly  and 
to  point  the  joints  carefully.  Milwaukee  cement  will  answer 
for  this  work.       Whitewashing  the  inner  face  of  such  a 
lining  will  be  sufficient  for  smoothness  and  tightness. 

4.  The  very  best  possible  lining  which  could  be  made 
would  be  secured  by  using  the  small,  thin  size  of  vitrified 
paving  brick.     These  may  be  set  on  edge,  to  reduce  both 
the  cost  and  the  number  of  cement  joints.    It  will  be  nec- 
essary to  tie  this  course  occasionally  to  the  main  wall  by 
turning  a  brick  endwise.       Rich  cement  mortar  should  be 
vised  and  the  joints  made  thin  but  thoroughly  filled  with 
the  mortar.    Such  a  lining  would  give  a  surface  like  a  stone 
jug,  thoroughly  air-tight  and  indefinitely  permanent. 

502.  Doors — The  jambs  may  best  be  made  of  3x6's  or 
SxS's  rabbetted  two  inches  deep  to  receive  the  door  on  the 
inside.  The  center  of  the  jambs  outside  should  be  grooved 
and  a  tongue  inserted  projecting  three-fourths  of  an  inch 
outward  to  set  back  into  the  mortar  and  thus  secure  a  thor- 
oughly air-tight  joint  between  the  wall  and  jamb. 

The  doors  are  best  made  as  described  under  the  stone  silo, 
of  two  layers  of  matched  flooring  with  paper  between. 


CONSTRUCTION  OF  BRICK-LINED  SILOS. 

to  the  all-masonry  silos  in  point  of  durability  and 
efficiency  must  be  ranked  the  masonry  lined  silos,  of  which 


40-i 


Rural  Architecture. 


there  are  several  types, as  follows:  (1)  Stone  silos,  jacketed 
with  wood;  (2)  concrete  lined  silos;  (3)  brick  lined  silos; 
(4)  lathed  and  plastered  silos. 


FIG.  200.— Showing  a   brick  lined  round  silo  with  bricks  set  on  edge  and 

Elastered    with    cement.    Dots    A,    A    show    where    an    iron    rod    may 
e  bedded  in  the  wall   to  prevent  spreading. 

Of  these  types  the  brick  lined  silo  is  likely  to  come  into 
the  more  general  use,  and  its  construction  will  be  described 
first. 


Construction  of  Brick-lined  Silos.  405 

503.  Foundation  and  Sill. — Like  the  brick  silo,  this  form 
should  have  a  stone  foundation,  wherever  it  is  practicable 
to  obtain  the  material  for  it.  Upon  this  should  first  be  laid 
the  sill  made  of  2x4's  cut  in  two-foot  lengths  with  the  ends 
beveled  so  that  they  may  be  toe-nailed  together  and  bedded 
in  cement  mortar  upon  the  wall  in  the  manner  represented 
in  Fig.  201.  The  sill  is  set  just  far  enough  back  from  the 
inside  of  the  wall  so  that  when  the  brick  are  laid  they  come 
flush  with  the  inside  of  thei  silo  wall. 


FIG.  201.— Showing  method  of  making  the  sill  of  brick  lined  and  of  round 
wood  silos.  B,  plan  of  studding  for  all-wood,  brick  lined  or  lathed 
and  plastered  silo. 

504.  Setting  Studding. — The  2x4  studding  are  next  set 
up  and  toe-nailed  to  the  sill.  A  stud  is  first  set  at  each  angle 
of  the  sill,  plumbed  and  stayed  from  a  post  set  in  the  center 
of  the  silo.    After  four  or  five  of  these  are  set  and  plumbed 
from  the  center  they  should  be  stayed  from  side  to  side  by 
tacking  to  them  a  strip  of  half-inch  sheeting  bent  around 
the  outside  as  high  up  as  a  man  can  reach,  taking  care  to 
get  each  stud  plumb  in  this  direction  before  staying.  After 
the  alternate  studs  have  been  set  up  in  this  manner  the 
intervening  ones  may  be  put  in  place,  toe-nailed  to  the  sill 
and  stayed  to  the  rib  holding  the  others  in  place. 

505.  Sheeting. — The  next  step  should  be  to  put  on  the 
outside  layer  of  sheeting  which,  for  all  of  the  silos  less  than 

26 


406  Rural  Architecture. 

30  feet  in  diameter,  should  be  three-eighths  inch  lumber 
made  by  buying  a  good  quality  of  fencing  and  taking  it  to 
the  mill  to  have  it  sawed  in  two.  The  usual  price  for 
sawing  fencing  in  two  in  this  way  is  $1.00  per  thousand. 
The  reason  for  getting  fencing  and  having  it  sawed  in  this 
manner  is  to  save  expense.  It  is  the  custom  of  dealers  to 
charge  the  same  price  for  half  inch  as  for  inch  lumber,  and 
hence  buying  good  fencing  and  having  it  sawed  reduces  the 
cost  just  one-half,  less  the  cost  of  sawing.  The  studding 
should  be  covered  inside  and  out  with  this  sheeting,  nailing 
thoroughly  with  8-penny  nails,  two  nails  in  each  board  at 
every  stud.  The  object  of  the  boards  is  to  act  as  hoops  and 
give  the  silo  the  needed  strength. 

506.  Siding. — If  the  silo  is  out  of  doors  it  will  need  to  be 
covered  with  house  siding  with  the  thick  edge  rabbetted,  or 
else  veneered  with  a  single  course  of  brick.     Several  silos 
have  been  sided    with  half-inch  lumber  with  both  edges 
beveled  at  an  angle  of  45  degrees  to  take  the  place  of  the 
rabbet.       This  method  gives  greater  strength,  but  is  not 
likely  to  keep  out  rain  as  thoroughly. 

507.  Lining. — The  brick  lining  of  the  silo  should  be  laid 
in  rich  Milwaukee,  Akron  or  Louisville  cement  mortar,  the 
bricks  being  previously  wet       The  most  rigid  lining  will 
be  secured  by  laying  the  brick  flatwise,  making  the  layer  4 
inches  thick,  but  with  one-half  the  amount  of  brick  they 
may  be  set  on  edge,  thus  considerably  lessening  the  cost. 
If  set  on  edge,  as  represented  in  Fig.  200,  a  row  of  spikes 
should  be  driven  into  the  studding  through  the  joints  of 
every  fourth  course  to  hold  the  brick  more  securely  in  place 
until  the  cement  has  had  time  to  season. 

The  mortar  should  not  be  made  more  than  one-fourth  of 
an  inch  thick  and  great  care  should  be  taken  to  leave  no 
open  space  anywhere.  The  necessity  of  plastering  the  wall 
may  be  avoided  by  filling  behind  each  brick  with  one-half 
an  inch  of  mortar,  which  will  keep  out  the  air  as  well  as  if 
on  the  front  side  and  there  will  be  the  additional 


Round  Plastered  Silos.  ±07 

of  the  cement  not  coming  in  direct  contact  with  the  silage 
juices.  If  care  is  taken  in  setting  the  brick  so  as  to  secure  a 
smooth  face,  pointing  the  joints  carefully,  it  will  not  be  nec- 
essary to  even  whitewash  the  wall  and  a  permanent  lining 
requiring  no  attention  will  thus  be  secured. 

In  this  form  of  silo  the  brick  may  have  one  face  filled 
with  coal  tar,  or  the  vitrified  paving  brick  may  be  used, 
giving  a  lining  wholly  air  tight  and  permanent. 


BOUND  PLASTERED   SILO. 

Where  brick  are  high,  lumber  low,  and  clean,  sharp  sand 
may  be  readily  obtained,  a  cement  plastered  lining  may  be 
made  to  take  the  place  of  the  brick  lining,  using  the  Mil- 
waukee, Akron,  Kosendale  or  Louisville  cement  in  making 
the  mortar.  The  first  coat  is  usually  made  with  hair  and 
a  little  lime  to  make  it  hang  to  the  -wall  better. 

There  are  a  good  many  of  these  lathed  and  plastered 
cylindrical'  silos  in  Racine  and  Kenosha  counties  in  Wis- 
consin, and  across  the  line  in  Illinois.  Some  of  these  have 
been  in  use  since  1889  and  have  given  good  satisfaction. 

508.  Construction.  —  The  frame  work  of  the  silo  should 
be  made  exactly  like  that  of  the  silo  with  brick  lining  ex- 
cept that  there  should  be  two  layers  of  half-inch  sheeting 
on  the  inside  with  a  layer  of  3-ply  Giant  P.  and  B.  paper 
between,  or  other  of  as  good  quality. 

After  the  woodwork  of  the  silo  has  been  completed  it 
should  be  lathed  and  plastered  with  a  cement  mortar  made 
of  1  of  cement  to  2.  of  sand. 

If  wood  lath  are  used  there  should  be  furring  strips  of 
lath  nailed  to  each  stud  up  and  down  and  the  lath  nailed 
through  these.  If  metal  lath  is  used  this  may  be  nailed 
directly  to  furring  strips  of  lath  nailed  to  the  studding  over 
the  lining  and  the  plastering  then  done. 

It  should  be  understood  that  it  would  not  dp  to  lath  and 
plaster  a  rectangular  wood  silo  because  the  springing  of  the 


408 


Rural  Architecture. 


walls  would  crack  the  cement.  It  should  be  understood 
further  that  on  account  of  the  fact  that  the  layer  of  cement 
is  so  thin  it  is  a  matter  of  greater  importance  to  keep  the 


FIG.  202. — Showing  an  all-wood  round  silo  on  stone  foundation.    H  rep- 
resents a  method  of  sawing  boards  for  the  conical  roof. 

surface  whitewashed  to  prevent  the  acid  from  softening  the 
cement  and  rendering  it  porous.  It  is  because  of  this  also 
that  two  layers  of  lining  with  paper  between  are  recom- 
mended. 


Construction  of  All-Wood  Silos. 


409 


CONSTRUCTION  OF  ALL  WOOD  SILOS. 

Up  to  the  present  time  more  silos  have  been  built  of  wood 
than  of  any  other  material,  and  since  1891,  the  majority  of 
wood  silos  built  have  been  after  the  model  represented  in 
Fig.  202.  Very  few  silos  of  the  rectangular  type  are  now 
built  unless  they  be  of  stone. 

509.  Foundation. — There  should  be  a  good,  substantial 
masonry  foundation  for  all  forms  of  wood  silos  and  the 
woodwork  should  everywhere  be  at  least  12  inches  above 
the  earth  to  prevent  decay  from  dampness.  There  are  few 
conditions  where  it  will  not  be  desirable  to  have  the  bottom 
of  the  silo  3  feet  or  more  below  the  feeding  floor  of  the 
stable  and  this  will  require  not  less  than  4  to  6  feet  of  stone, 
brick,  or  concrete  wall.  For  a  silo  30  feet  deep  the-  founda- 
tion wall  of  stone  should  be  1.5  to  2  feet  thick. 


FIG.  203.— Showing  two  methods  of  placing  the  wood,  brick  lined  or 
lathed  and  plastered  silo  on  a  stone  foundation.  A-  shows  the  silo 
Bet  with  upper  portion  flush  with  the  inside  of  the'  stone  wall,  and 
B  shows  the  upper  portion  flush  with  the  outside  of  the  stone  wall. 

The  inside  of  the  foundation  wall  may  be  made  flush 
with  the  woodwork  above,  as  represented  in  Fig.  203  A,  or 


Rural  Architecture. 

the  building  may  stand  in  the  ordinary  way,  flush  with  the 
outside  of  the  stone  wall,  as  represented  in  Fig.  203  B.     In 

-  both-  cases  the  wall  should  be  finished  sloping  as  shown  in 
the  drawings. 

j 

510.  Cementing  the  Bottom. — After  the  silo   has  been 

completed  the  ground  forming  the  bottom  should  be  thor- 
oughly tamped  so  as  to  be  solid  and  then  covered  with  two 

•  or  three  inches  of  good  concrete  made  of  1  of  cement  to  3 
or  4  of  sand  and  gravel.    The  amount  of  silage  which  will 
spoil  on  a  hard  clay  floor  will  not  be  large,  but  enough  to 
pay  a  good  interest  on  the  money  invested  in  the  cement 
floor.    If  the  bottom  of  the  silo  is  in  dry  sand  or  gravel  the 
cement  bottom  is  imperative  to  shut  out  the  soil  air. 

511.  Tying  Top  of  Wall. — In  case  the  wood  portion  of  the 
silo  rises  24  or  more  feet  above  the  stone  work  and  the 
diameter  is  more  than  18  feet  it  will  be  prudent  to  stay  the 
top  of  the  wall  in-some  way.  »"'N 

If  the  woodwork  rises  from  the  outer  edge  of  the  wall, 
then  building  the  wall  up  with  cement  so  as  to  cover  the 
sill  and  lining  as  represented  in  Fig.  ^2Q7  will  give 
the  needed  strength,  because  the  wood- work  will  act  as  a 
hoop;  but  if  the  silo  stands  at  the  inner  face  of  the  wall,  it 
will  be  best  to  lay  pieces  of  ironlrod  in  the  wall  near  the  top 
to  act  as  a  hoop. 

Where  the  stone  portion  of  the  silo  is  high  enough  to 
need  a  door  it  is  best  to  leave  enough  wall  between  the  top 
and  the  sill  to  allow  a  tie  rod  of  iron  to  be  bedded  in  this 
portion.  So,  too,  the  lower  door  in  the  woodwork  of  the 
silo  should  leave  a  full  foot  in  width  below  it  of  lining  and 
siding  uncut  to  act  as  a  hoop";  where  the  pressure  is 
strongest. 

512.  Sills  and  Studding. — The  sill  in  the  all-wood  silo 
may  be  made  of  a  single  2x4,  cut  in  2-foot  lengths,  in  the 
manner  represented  in  Fig.  201  and  described  under  the 
brick  lined  silo. 


Construction  of  All'-Wood  Silos. 


411 


1:  'Tne  studding  of  tlie  all-wood  round  silo  need  not  be 
largerthan  2x4  unless  the  diameter  is  to  exceed  30  feet,  but 
they  should  be  set  as  close  together  as  one  foot  from  center 
to  center,  as  represented  in  Fig.  201,  B.  This  number  of 
studs  is  not  required  for  strength  but  they  are  needed  in 
order  to  bring  the  two  layers  of  lining  very  close  together 
so  as  to  press  the  paper  closely  and  prevent  air  from  enter- 
ing where  the  paper  laps. 


o 


0 


tffiG.'  204.— Showing  ,the  construction  of  the -door  for  the  all-wood  silo. 
G  is  a  cross-section  of  the  door  resting  against  the  door  jamb,  which 

-        is    provided    with  ,  a    gasket    of    three-ply    ruberoid    roofing    and    held 

'  in  place  with   four  lag  bolts   and   washers,    the   door  opening   on   the 

inside.    F   is   a   front   view   of   the   door   made  of  two   layers  of   four 

inch  or  six  inch  tengued  and  grooved  -flooring  with  a  layer  of  three- 

'       ply  acid  and  water  proof  P.  &  B.  paper  between. 

To  stay  the  studding  a  post  should  be  set  in  the  ground 
in  the  center  of  the  silo  long  enough  to  reach  about  5  feet 
above  the  sill  and  to  this  stays  may  be  nailed  to  hold  ih 
place  the  alternate  studs  until  the  lower  5  feet  of  outsidb 


Rural  Architecture. 

sheeting  lias  been  put  on.  The  studs  should  be  set  first  at 
the  angles  formed  in  the  sill  and  carefully  stayed  and 
plumbed  on  the  side  toward  the  center.  When  a  number 
of  these  have  been  set  they  should  be  tied  together  by 
bending  a  strip  of  half-inch  sheeting  around  the  outside  as 
high  up  as  a  man  can  reach,  taking  care  to  plumb  each  stud 
on  the  side  before  nailing.  When  the  alternate  studs  have 
been  set  in  this  way  the  balance  may  be  placed  and  toe- 
nailed  to  the  sill  and  stayed  to  the  rib,  first  plumbing  them 
sideways  and  toward  the  center. 

On  the  side  of  the  silo  where  the  doors  are  to  be  placed 
the  studding  should  be  set  double  and  the  distance  apart  to 
give  the  desired  width.  A  stud  should  be  set  between  the 
two  door  studs  as  though  no  door  were  to  be  there  and  the 
doors  cut  out  at  the  places  desired  afterwards.  The  con- 
struction of  the  door  is  represented  in  Fig.  204. 

513.  Sheeting  and  Siding. — The  character  of  the  siding 
and  sheeting  will  vary  considerably  according  to  conditions 
and  size  of  the  silo. 

Where  the  diameter  of  the  silo  is  less  than  18  feet  inside 
and  not  much  attention  need  be  paid  to  frost,  a  single  layer 
of  beveled  siding,  rabbetted  on  the  inside  of  the  thick  edge 
deep  enough  to  receive  the  thin  edge  of  the  board  below, 
will  be  all  that  is  absolutely  necessary  on  the  outside  for 
strength  and  protection  against  weather.  This  statement 
is  made  on  the  supposition  that  the  lining  is  made  of  two 
layers  of  fencing  split  in  two,  the  three  layers  constituting 
the  hoops. 

If  the  silo  is  larger  than  18  feet  inside  diameter,  there 
should  be  a  layer  of  half-inch  sheeting  outside,  under  the 
siding. 

If  basswood  is  used  for  siding  care  should  be  taken  to 
paint  it  at  once,  otherwise  it  will  warp  badly  if  it  gets  wet 
before  painting. 

In  applying  the  sheeting  begin  at  the  bottom,  carrying 
the  work  upward  until  staging  is  needed,  following  this  at 
once  with  the  siding.  Two  8-penny  nails  should  be  used 


Construction  of  All-Wood  Silos.  413 

in  eacli  board  in  every  stud,  and  to  prevent  the  walls  from 
getting  "out  of  round"  the  succeeding  courses  of  boards 
should  begin  on  the  next  stud,  thus  making  the  ends  of  the 
boards  break  joints. 

When  the  stagings  are  put  up  new  stays  should  be  tacked 
to  the  studs  above,  taking  care  to  plumb  each  one  from 
side  to  side ;  the  siding  itself  will  bring  them  into  place  and 
keep  them  plumb  the  other  way  if  care  is  taken  to  start  new 
courses  as  described  above. 

514.  Forming  the  Plate. — When  the  last  staging  is  up  the 
plate  should  be  formed  by  spiking  2x4's,  cut  in  two-foot 
lengths,  in  the  manner  of  the  sill,  and  as  represented  in  Fig. 
205,  down  upon  the  tops  of  the  studs,  using  two  courses, 
making  the  second  break  joints  with  the  first. 


FIG.  205.— Showing  construction  of  conical  roof  of  round  silo  where  rafters 
are  not  used.  The  outer  cir?le  is  the  lower  edge  of  the  roof,  the 
second  circle  is  the  plate,  the  third  and  fourth  circles  are  hoops 
to  which  the  roof  boards  are  nailed.  The  view  is  a  plan  looking  up 
from  the  under  side. 

515.  Lining  for  Wood  Silos — There  are  several  ways  of 
making  a  good  lining  for  the  all  wood  round  silo,  but 
whichever  method  is  adopted  it  must  be  kept  in  mind  that 


'414  Rural  Architecture. 

there  are  two  very  important  ends  to  be  secured  with  cer- 
tainty. These  are  (1)  a  lining  which  shall  be  and  remain 
strictly  air  tight,  (2)  a  lining  which  will  be  reasonably 
permanent. 

Galvanized  Iron  in  Silo  Lining. — The  tightest  lining  for 
a  wood  silo  may  be  made  with  a  light  weight  of  galvanized 
iron,  No.  28  to  No.  32.  Where  the  silos  are  18  feet  in 
diameter  or  less  this  may  be  put  direetly  upon  the  studding, 
buying  the  strips  8  feet  long  and  36  inches  wide,  so  as  to 
be  nailed  on  up  and  down  and  exactly  cover  the  space  be- 
tween three  or  four  studs.  Headers  should  be  put  in  every 
8  feet  to  nail  the  ends  of  the  sheets  to  between  the  studs, 
and  these  are  best  when  sawed  to  the  curve  of  the  silo.  The 
,  metal  should  be  put  on  with  roofing  nails,  nailing  close  so 
as  to  make  the  joints  tight. 

After  the  metal  is  in  place  it  should  be  given  a  heavy 
coat  of  asphalt  paint,  taking  special  care  to  make  it  heavy 
where  the  nails  and  laps  come  so  as  to  shut  out  the  air. 

When  the  metal  is  in  place  and  painted  it  should  be 
covered  with  a  layer  of  sheeting  made  the  same  as  that  used 
outside,  by  splitting  good  fencing  in  two.  The  object  of 
this  layer  of  sheeting  is,  first  to  take  the  pressure  of  the 
silage ;  second,  to  act  as  a  hoop  for  strength,  and  third,  to 
keep  the- silage  from  softening  and  wiping  the  plaint  from 
the  metal  lining.  Were  it  not  for  the  fact  that  t*he  heat  of 
the  silage  tends  to  soften  the  paint,  and  its  settling  to  wipe 
it  off,  it  would  be  better  to  let  the  metal  come  next  to  the 
silage. 

Where  the  silo  is  more  than  18  feet  in  diameter  it  will  be 
best  to  use  two  layers  of  fencing  split  in/ two,  placing  the 
galvanized  iron  between  the  two  layers.  In  these  cases  the 
sheets  of  metal  may  be  put  on  horizontally,  using  those.  3j6 
inches  wide. 

All  Wood  Lining  of  4-inch  Flooring — If  one  is  willing 
to  permit  a  loss  of  10  to  12  per  cent,  of  the  silage  by  heat- 
ing, then  a  lining  of  tongued  and  grooved  ordinary  4-inch 
white  pine  flooring  may  be  made  in  the  manner  repre- 
sented in  Fig.  206,  where  the  flooring  runs  up  and  down. 


Construction  of  All-Wood  Silos. 


415 


When  this  lumber  is  put  on  in  the  seasoned  condition  a 
single  layer  would  make  tighter  walls  than  can  be  secured 
with  the  stave  silo  where  the  staves 
are  neither  beveled  nor  tongued  and 
grooved. 

In  the  silos  smaller  than  18  feet  in- 
side diameter  the  two  layers  of  boards 
outside  will  give  the  needed  strength, 
but  when  the  silo  is  larger  than  this 
and  deep  there  would  be  needed  a 
layer  of  the  split  fencing  on  the  inside 
for  strength ;  and  if  in  addition  to  this 
there  is  added  a  layer  of  3-ply  Giant 
P.  and  B.  paper,  a  lining  of  very  su- 
perior quality  would  be  thus  secured. 

Lining  of  Half-inch  Boards  and 
Paper. — Where  paper  is  used  to  make 
the  joints  between  boards  air  tight,  as 
represented  in  Fig.  207,  it  is  ex- 
tremely important  that  a  quality 
which  will  not  decay  and  which  is 
both  acid  and  water-proof  be  used.  A 
paper  which  is  not  acid  and  water- 
proof will  disintegrate  at  the  joints 
in  a  very  short  time  and  thus  leave  the 
lining  very  defective. 

Great  care  should  be  taken  to  have 
the  two  layers  of  boards  break  joints 
at  their  centers,  and  the  paper  should 

Ian  not  lp«;q  tVian  8  to  1  9,  iriplips  FIG.   206.  —  Showiner    Use 

GS-  construction  of  ibe  all-wood 

The  great  danger  with  this  type  of  silo  where  the  linine  is  made 

..     .  .-in  i         iii  1  of  ordinary  four  inch  fl<x-r- 

hning  will  be  that  the  boards  may  not  ins  running  up  and  down, 

,,  -,  ,.  •*  .          and  nailed  to  girts  cut  in 

press  the  tWO  layers  OI  paper  together  between  the  studding  every 
1  1,    U    4.    4.1.    4.  •  four  feet. 

close  enough  but  that  some  air  may 

rise  between  the  two  sheets  where  they 

overlap  and  thus  gain  access  to  the  silage.     It  would  be  an 

excellent  precaution  to  tack  down  the  edges  of  the  paper 


Rural  Architecture. 


closely  with  small  carpet  tacks  where  they  overlap,  and  if 
this  is  done  a  lap  of  2  inches  will  be  sufficient. 


PIG.  207.— D,  Showing  method  of  constructing  the  all-wood  round  silo 
and  connecting  it  with  the  wall  flush  with  the  outside.  This  figure 
shows  the  most  substantial  form  of  construction  with  three  layers 
of  half-inch  lumber  and  two  layers  of  three-ply  acid  and  water 
proof  P.  &  B.  paper  between  them.  A  very  excellent  silo  is  made 
after  this  plan  omitting  the  inner  layer  of  lining  and  paper  and 
the  layer  of  paper  on  the  outside.  With  small  silos  15  feet  in  diam- 
eter only  the  siding  on  the  outside  is  necessary  for  strength  and 
protection  against  weather.  E,  Showing  method  of  construction  for 
ventilating  the  spaces  between  the  studding  in  all-wood  and  lathed 
and  plastered  silos.  The  lower  portion  shows  the  intakes  of  fresh 
air  from  the  outside  at  the  bottom,  and  the  upper  portion  shows 
where  the  air  enters  the  silo  at  the  plate  to  pass  out  at  the  ventilator 
in  tlie  roof. 

Such  a  lining  as  this  will  be  very  durable  because  the 
paper  will  keep  all  the  lumber  dry  except  the  inner  layer 
of  half-inch  boards,  and  this  will  be  kept  wet  by  the  paper 
and  silage  until  empty  and  then  the  small  thickness  of  wood 
will  dry  too  quickly  to  permit  rotting  to  set  in. 

A  still  more  substantial  lining  of  the  same  type  may  be 
secured  by  using  two  layers  of  paper  between  three  layers 
of  boards,  as  represented  in  Fig.  207,  and  if  the  climate  is 


Construction  o£  All-Wood  Silos.  417 

not  extremely  severe,  or  if  the  silo  is  only  to  be  fed  from 
in  the  summer,  it  would  be  better  to  do  away  with  the  layer 
of  sheeting  and  paper  outside,  putting  it  on  the  inside,  thus 
securing  two  layers  of  paper  and  three  layers  of  boards  for 
the  lining  with  the  equivalent  of  only  2  inches  of  lumber. 

516.  Construction  of  Eoof. — The  roof  of  cylindrical  siloa 
may  be  made  in  several  ways,  but  the  simplest  type  of  con- 
struction and  the  one  requiring  the  least  amount  of  mater- 
ial is  the  cone,  represented  in  Figs.  202  and  205. 

If  the  silo  is  not  larger  than  15  feet  inside  diameter  no 
rafters  need  be  used,  and  only  a  single  circle,  like  that  in 
the  center  of  Fig.  205.  This  is  made  of  2-inch  stuff  cut 
in  section  in  the  form  of  a  circle  and  two  layers  spiked  to- 
gether, breaking  joints. 

517.  Ventilation  of  Silos. — Every  silo  which  Has  a  roof 
should  be  provided  with  ample  ventilation  to  keep  the 
underside"  of  the  roof  dry  and  in  the  case  of  wood  silos,  to 
prevent  the  walls  and  lining  from  rotting.       One  of  the 
most  serious  mistakes  in  the  early  construction  of  wood 
silos  was  the  making  of  the  walls  with  dead-air  spaces 
which,  on  account  of  the  dampness  from  the  silage,  lead  to 
rapid  "dry  rot"  of  the  lining. 

In  the  wood  silo  and  in  the  brick  lined  silo  it  is  important 
to  provide  ample  ventilation  for  the  spaces  between  the 
studs,  as  well  as  for  the  roof  and  the  inside  of  the  silo,  and 
a  good  method  of  doing  this  is  represented  in  Fig.  207,  E, 
where  the  lower  portion  represents  the  sill  and  the  upper  the 
plate  of  the  silo.  Between  each  pair  of  studs,  where  needed, 
a  one  and  one-fourth  inch  auger  hole  to  admit  air  is  bored 
through  the  siding  and  sheeting  and  covered  with  a  piece 
of  wire  netting  to  keep  out  mice  and  rats.  At  the  top  of 
the  silo  on  the  inside  the  lining  is  only  covered  to  within 
two  inches  of  the  plate  and  this  space  is  covered  with  wire 
netting  to  prevent  silage  from  being  thrown  over  when 
filling.  This  arrangement  permits  dry  air  from  outside  to 
enter  at  the  bottom  between  each  pair  of  studs  and  to  pass 


418  Rural  Architecture. 

up  and  into  the  silo,  thus  keeping  the  lining  and  studding 
dry  and  at  the  same  time  drying  the  under  side  of  the  roof 
and  the  inside  of  the  lining  as  fast  as  exposed.  In  those 
cases  where  the  sill  is  made  of  2x4's  cut  in  2-foot  lengths 
there  will  be  space  enough  left  between  the  curved  edge 
of  the  siding  and  sheeting  and  the  sill  for  air  to  enter,  so 
that  no  holes  need  be  bored  as  described  above  and  repre- 
sented in  Fig.  207  E.  The  openings  at  the  plate  should  al- 
ways be  provided  and  the  silo  should  have  some  sort  of  ven- 
tilator in  the  roof.  This  ventilator  may  take  the  form  of  a 
cupola  to  serve  for  an  ornament  as  well,  or  it  may  be  a 
simple  galvanized  iron  pipe  12  to  24  inches  in  diameter, 
rising  a  foot  or  two  through  the  peak  of  the  roof. 

518.  Painting  Silo  Lining. — It  is  impossible  to  so  paint  a 
wood  lining  that  it  will  not  become  wholly  or  partly  satur- 
ated with  the  silage  juices.  This  being  true,  when  the 
lining  is  again  exposed  when  feeding  the  silage  out,  the 
paint  greatly  retards  the  drying  of  the  wood  work  and  the 
result  is  decay  sets  in,  favored  by  the  prolonged  dampness. 
For  this  reason  it  is  best  to  leave  a  wood  lining  naked  or  to 
use  some  antiseptic  which  does  not  form  a  water  proof  coat. 


THE  STAVE  OR  TANK  SILO. 

We  have  examined  personally  19  stave  silos  and  have 
made  a  careful  study  of  the  unavoidable  losses  in  one  of 
these.  We  have  also  studied  the  unavoidable  loss  in  two 
kinds  of  small  stave  silos.  As  a  result  of  these  observations 
it  has  been  demonstrated  that  there  are  several  very  serious 
objections  to  stave  silos  intended  as  permanent  buildings 
out  of  doors.  Some  of  these  are  stated  below : 

1.  When  the  silo  is  empty  the  staves  shrink  and  loosen 
the  hoops  and  in  this  condition  the  wind  racks  the  building, 
getting  it  out  of  round,  out  of  plumb,  and  out  of  place  upon 
the  foundation.  It  is  much  more  easily  blown  down  than 


Construction  of  Stave  Silos.  419 

other  forms  of  silos.  Two  of  the  fourteen  out-of-door  silos 
visited  had  been  blown  down;  one  of  these  was  abandoned 
and  the  hoops  sold  to  another  farmer;  the  other  was  set  up 
again  at  the  expense  of  a  day's  drive  for  new  staves  and  get- 
ting the  carpenters  to  set  it  up,  the  accident  happening  just 
as  they  were  ready  to  fill  the  silo. 

A  third  silo  of  the  fourteen  out-of-doors  we  visited  had 
moved  on  the  foundation  so  much  that  I  could  put  my  arm 
up  through  between  the  stone  wall  and  the  outside  of  the 
staves.  This  silo  had  been  stayed  to  the  end  of  the  barn, 
using  fence  wire  for  guy  rods. 

Three  others  of  the  fourteen  outrof-door  stave  silos  had 
been  found  so  unsatisfactory  that  they  were  subsequently 
lined  on  the  inside  to  prevent  the  silage  from  spoiling,  and 
in  two  of  these  three  the  inner  lining  has  rotted  out  on  ac- 
count of  the  dampness  which  the  outside  staves  confines. 

2.  There  is  great  danger  of  the  hoops  being  broken  by 
the  intense  pressure  of  the  silage  increased  by  the  swelling 
of  the  staves.  In  one  of  the  silos  visited  eight  out  of  ten 
hoops  on  one  side  of  the  silo  and  six  out  of  ten  on  the  oppo- 
site side  had  sheared  in  two  the  2x4's  used  lor  lugs;  but,  by 
a  fortunate  coincidence,  two  of  the  ten  hoops  remained 
intact  to  hold  the  silo  up,  assisted  by  some  half -inch  boards 
which  had  been  bent  around  the  inside  of  the  silo  at  the  top 
to  prevent  the  staves  from  falling  in. 

In  another  silo  where  4x4  oak  pieces  had  been  used  as 
lugs,  the  2-inch  iron  washers  had  been  crushed  their  full 
depth  of  onte-half  inch  into  the  hard  wood  and  two  of  the 
pieces  of  wood  had  been  badly  injured  by  the  severe  strain 
upon  them-. 

In  a  fourth  silo  where  the  hoops  were  provided  with  iron 
lugs  the  staves  on  one  side  had  been  thrown  into  the  silo  by 
the  swelling  of  the  wood. 

It  is  urged  by  the  advocates  of  these  silos  that  with  a 
little  care  and  judgment  the  nuts  of  the  hoops  may  be 
tightened  or  loosened  as  needed  and  such  accidents  averted. 
There  is  enough  truth  in  this  statement  to  induce  many 
farmers  with  limited  means  to  take  the  risk,  but  life  is  too 


420  Rural  Architecture. 

short  and  there  are  too  many  other  things  to  engross  the  at- 
tention of  good  farmers  for  them  to  lie  awake  nights  won- 
dering whether  the  silo  hoops  are  too  tight  or  too  loose. 

3.  Staves  do  not  contain  the  same  amount  of  sapwood  in 
all  parts  and  for  this  reason  shrink  unequally,  with  the  re- 
sult that  after  3  or  4  years'  use  there  are  places  which  do 
not  close  up  tightly  on  swelling  and  which  open  again  on 
the  sunny  side  of  the  silo,  and  thus  admit  air,  even  where 
the  silage  is  in  contact  with  them. 

Three  of  the  silos  visited  showed  these  peculiarities,  and 
in  one  of  them  visited  last  win'ter  we  could  see  through  be- 
tween several  staves  on  the  south  side  of  the  silo  close  to  the 
silage' surf  ace,  on  the  inside. 

4.  The  expansion  and  contraction  of  the  staves  during 
wetting  by  the  silage  and  drying  when  the  silo  is  empty 
makes  it  difficult  to  securely  anchor  a  permanent  roof  and 
impossible  to  connect  the  staves  permanently  with  the  foun- 
dation, so  as  to  be  air-tight.    Something  must  be  done  each 
season  to  cement  the  joints  between  the  staves  and  foun- 
dation or  air  will  enter. 

5.  There  is  no  reason  to  hope  that  good  silage  with  small 
losses  in  dry  matter  can  be  made  in  the  stave  silos  which 
are  not  carefully  constructed   of  good  lumber  with  the 
staves  both  beveled,  and  tongued  and  grooved.    It  is  really 
more  difficult  to  make  a  stave  silo  air  tight  than  it  is  to 
make  a  tank  water-tight,  and  we  have  found  by  careful 
tests  that  the  unavoidable  losses  in  a  new  stave  silo  next  to 
the  walls  were  as  high  as  24  to  28  per  cent. 

513.  Construction  of  Stave  Silos — There  are  three  meth- 
ods adopted  in  the  construction  of  these  silos.  The  best 
and  only  one  which  should  be  used  in  the  permanent  silo 
is  that  represented  in  Fig.  208,  where  the  staves  are  both 
beveled  and  tongued-and-grooved ;  the  second  is  where  the 
staves  are  beveled  so  that  the  flat  surfaces  fit  together  ac- 
curately as  water  tanks  are  made;  the  third  plan  uses  the 
lumber  without  either  beveling  or  tonguing-and-grooving, 
and  this  both  observation  and  principles  of  construction  in- 


Construction  of  Stave  Silos. 


421 


dicate  should  be  adopted  with  very  great  hesitation  and  as 
a  temporary  makeshift  only  until  more  experience  and  ex- 
act knowledge  has  been  obtained  regarding  their  perma- 
nent efficiency. 


FIG.  208.— Showing  the  construction  of  the  stave  silo.  A  shows  the  silo 
complete  on  stone  foundation  with  four  feeding  doors.  B  is  cross- 
section  of  four  staves  showiug  how  they  are  tongued  and  grooved 
to  make  them  air  tight.  C  shows  a  method  of  splicing  staves.  D 
shows  iron  lugs  for  tightening  hoops.  F  is  front  view  of  door  viewed 
from  outside.  G  cross-section  of  same.  E  is  a  vertical  section  show- 
ing the  shoulder  against  which  the  door  rests,  and  upon  which  should 
be  a  gasket  of  three-ply  ruberoid  roofing.  The  door  should  also  be 
drawn  tight  against  it  with  four  lag  bolts  and  washers,  opening  from 
the  inside. 

This  third  plan  has  been  recommended  because  the  first 
cost  is  relatively  low  and  because  it  is  assumed  that  the  pres- 
27 


422  Rural  Architecture, 

sure  due  to  the  swelling  of  the  wood  and  the  rigidity  of  the 
hoops  will  result  in  crushing  the  edges  of  the  staves  to- 
gether so  as  to  make  a  sufficiently  tight  joint  to  preserve 
the  silage. 

i  520.  Lumber  for  Staves — The  lumber  selected  for  the 
staves  of  this  type  of  silo  should  be  of  the  grade  known  com- 
mercially as  "tank  stuff,"  and  lumber  freest  from  knots 
and  straightest  grained  is  best.  Wood  is  quite  air-tight 
under  low  pressures  in  directions  across  the  grain  but  along 
the  grain  the  air  passes  more  or  less  freely.  The  Washing- 
ton cedar  appears  to  be  an  excellent  wood  for  this  purpose, 
as  it  shrinks  much  less  than  the  pine  after  the  silage  is  re- 
moved and,  for  this  reason,  the  building  will  be  much  more 
stable  when  empty  and  less  liable  to  burst  the  hoops  when 
filled. 

Where  the  silo  is  to  be  deeper  than  can  readily  be  secured 
with  single  lengths  of  lumber  the  staves  may  be  spliced  in 
the  manner  represented  at  C,  Fig.  208,  where  a  saw-cut  is 
made  in  the  ends  of  the  two  staves  and  a  piece  of  galvanized 
iron,  a  little  wider  than  the  stave  is  slipped  into  it.  This 
crushes  into  the  wood  on  the  sides  and  forms  a  water  tight 
joint 

521.  Foundation  of  Stave  Silo — On  account  of  the  ten- 
dency of  the  stave  silo  to  work  off  from  the  wall  when 
empty  a  flat  cement  floor  has  been  recommended,  made  of 
sand  and  gravel  or  crushed  rock,  forming  a  bed  of  concrete 
about  12  inches  thick.      This  is  perhaps  as  good  as  can  be 
done  under  the  circumstances  but  it  precludes  the  exten- 
sion of  the  silo  into  the  ground. 

If  the  silo  stands  upon  a  stone  wall,  as  represented  in  Fig. 
208,  it  will  be  prudent  to  have  a  shoulder  jutting  into  the. 
silo  as  much  as  2  inches  and  a  similar  amount  on  the  out- 
side, to  permit  of  some  movement  on  the  foundation. 

522.  Hoops  for  Stave  Silo. — Five-eighths  inch  round  iron 
rods,  in  about  16-foot  lengths,  form  the  best  hoops  and  they 


Pit  Silos.  £23 

should  be  provided  with  long  threads  and  joined  with  iron 
lugs  and  nuts,  as  represented  in  D,  Fig.  208.  The  iron  lugs 
should  always  be  used  in  preference  to  the  2x4's  or  4rx4;s 
because  they  are  better  in  every  way.  So,  too,  should  they 
be  used  in  preference  to  posts  set  up  against  the  silo  outside 
or  shaped  to  act  as  a  part  of  the  staves  as  has  been  recom- 
mended. In  visiting  over  100  silos  in  1891  it  was  found 
that  wherever  a  silo  lining  had  a  heavy  timber  back  of  it, 
the  holding  of  dampness  caused  rotting  there  in  three  or 
four  years,  and  it  is  quite  certain  that  the  use  of  iron  lugs 
is  the  safest  way  to  avoid  this  danger  in  stave  silos. 

523.  Doors  for  Stave  Silos — A  good  method  of  construct- 
ing doors  for  the  stave  silo  is  represented  in  Fig.  208. 
Two  inch  lumber  is  bolted  to  the  staves  on  the  outside,  pro- 
jecting two  inches  into  the  doorway  all  around,  thus  form- 
ing a  rabbet  against  which  the  door  may  rest.     A  strip  of 
thick  ruberoid  roofing  should  be  used  on  the  rabbet  under 
the  door  and  the  door  drawn  down  tight  with  £our  lag  bolts 
and  washers. 

A  common  way  of  making  these  doors  is  to  cut  the  staves 
out  on  a  bevel  and  make  the  door  fit  into  this  beveled  cut 
directly.  If  the  work  is  carefully  done  and  then,  at  the  time 
of  filling,  if  the  face  of  the  bevel  is  plastered  with  a  thick 
coat  of  puddled  clay  and  the  door  forced  tightly  into  this  a 
fairly  close  joint  may  be  secured. 

524.  Pit  Silos. — In  localities  where  both  lumber   and 
masonry  are  expensive  or  cannot  be  had,  and  where  the  soil 
is  of  such  a  character  that  a  pit  15  to  20  feet  deep  may  be 
sunk  in  the  ground,  a  good  silo  may  be  made  in  this  way. 
The  most  serious  objection  to  such  a  silo  is  the  incon- 
venience of  removing  the  silage  to  feed. 

If  the  soil  is  of  such  a  character  that  it  will  not  cave  in 
the  pit  may  be  made  circular  in  form,  of  the  desired  size 
and  depth  and  then  plastered  with  cement  in  the  manner 
of  a  cistern.  If  there  is  a  little  difficulty  in  the  walls  stand- 


Rural  Architecture'. 


ing  the  pit  may  be  made  with  sloping  sides,  smallest  at  the 
bottom. 

In  using  such  a  silo,  especially  when  filling  it,  care  should 
be  observed  in  going  into  it  when  there  is  a  possibility  that 
carbonic  acid  has  accumulated  to  a  dangerous  extent,  There 
need  be  no  danger  in  using  such  a  silo  if  caution  is  observed 
as  stated  on  page  427. 

525.  Weight  of  Silage  per  Cubic  Foot. — The  weight  of 
corn  silage  increases  with  the  depth  below  the  surface,  with 
the  amount  of  water  in  the  silage,  and  with  the  diameter  of 
the  dlo.  In  silos  of  small  diameters  the  amount  of  surface 
in  the  Avail  is  so  much  greater  in  proportion  to  the  silage 
contained  that  the  friction  on  the  sides  has  more  influence 
in  preventing  the  settling  of  the  silage.  In  the  following 
table  will  be  found  the  weights  of  silage  per  cubic  foot  in 
round  silos  given  for  different  depths  and  the  mean  weight 
of  silage  above  the  given  depth: 

Table  showing  the  computed  weight  of  well  matured  corn  sil- 
age at  different  distances  below  the  surface,  and  the  com- 
puted mean  weight  for  silos  of  different  depths,  two  days 
after  filling. 


Weight 

f\f  oil 

Mean 

Weight 

Mean 

Weight 

Mean 

Depth 
of 

OI  SH- 

age  at 

weight 
of  sil- 

Depth 
of 

of  silage 
at 

weight  of 
silage 

Depth 
of 

of  silage 
at 

weight  of 
silage 

silage. 

cut 
depths. 

age  per 
cu.  ft. 

silage 

different 
depths. 

per  cubic 
foot. 

silage. 

different 
depths. 

per  cu. 
foot. 

Feet. 

Lbs. 

Lbs. 

Feet. 

Lbs. 

Lbs. 

Feet. 

Lbs. 

Lbs. 

1 

18.7 

18.7 

13 

37  3 

28.3 

25 

51.7 

36.5 

2 

20  4 

19.6 

14 

38  7 

29.1 

26 

52.7 

37.2 

3 

22.1 

20.6 

15 

40.0 

29.8 

27 

53.6 

37.8 

4 

23.7 

21.2 

16 

41  3 

30.5 

28 

54.6 

38.4 

5 

25.4 

22.1 

17 

42  6 

31.2 

29 

55  5 

39.0 

6 

27.0 

2i  9 

18 

4^  8 

31  9 

30 

58.4 

39.6 

7 

28.5 

23.8 

19 

45.0 

32.6 

31 

57.2 

40.1 

8 

3(1  1 

24.5 

20 

46.2 

33  3 

32 

58  0 

40.7 

9 

31.6 

25.3 

21 

47.4 

33.9 

33 

58.8 

41.2 

10 

33.1 

26.1 

22 

48.5 

34.6 

34 

59  6 

41.8 

11 

34.5 

26.8 

23 

49.6 

35.3 

35 

60.3 

42.3 

12 

35.9 

27.6 

24 

50.6 

35.9 

36 

61.0 

42.8 

526.  Capacity  of  Silos. — The  amount  of  silage  which  may 
be  stored  in  a  silo  increases  in  a  higher  ratio  than  the  depth 


Capacity  of  Silos. 


425 


increases.    A  silo  36  feet  deep  will  store  nearly  5  times  the 
amount  of  feed  that  one  12  feet  deep  will. 

Doubling  the  diameter  of  a  silo  increases  its  capacity 
more  than  fourfold  and  a  silo  30  feet  in  diameter  will  hold 
more  than  9  times  as  much  as  one  10  feet  in  diameter  and 
of  the  same  depth.  It  is  clear  from  this  that  small  silos 
must  be  relatively  more  costly  that  those  of  larger  diameter. 

Table  giving  the  approximate  capacity  of  cylindrical  silos  for 
well  matured  corn  silage,  in  tons. 


Depth, 
Faet. 

INSIDE  DIAMETER  IN  FEET. 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

163.4 
174.7 
186  8 
199.3 
211  5 

26 

20. 
21. 
22. 
23. 
24. 
25. 
26. 
27. 
28. 
19. 
•M. 
31. 
32. 

58.84 
62.90 
67.35 
71.73 
76  12 

66.95 
71.56 
76.52 
81.61 
86  61 

75.58 
80.79 
86.38 
92.14 
97.78 

81.74 
90  57 
96.84 
103.3 
109  6 

94.41 
100.9 
107.9 
115.1 
122  1 

104.6 
111.8 
119.6 
127.5 
135  3 

115.3 
123.3 
131.8 
140.6 
149  2 

126.6 
135.3 
144.7 
154.3 
163  7 

138.3 
147.9 
158.1 
168.7 
179  0 

150.6 
161.0 
172.2 
183.6 
194  9 

176.8 
189.0 
202.1 
215  5 
228  7 

80.62 
85.45 
90.17 
94.99 
99.92 
105.0 
109.8 
115.1 

8>.64 
97.23 
102.6 
108.1 
113  7 
119.4 
124.9 
135.9 

103.6 
109.8 
115.8 
122.0 
128.3 
134.8 
141.1 
147.8 

116.1 
123.0 
129  8 
136.8 
143.9 
151  1 
158.2 
165.7 

129.3 
137.1 
144.7 
152.4 
160.3 
168.4 
176.2 
184.6 

143.3 
151.9 
160.3 
168.9 
177.6 
186.6 
195.2 
201.6 

158.0 
167.5 
176.7 
186.2 
195.8 
205.7 
215.3 
225.5 

173.4 
183.8 
194  0 
201.3 
214.9 
225.8 
236.3 
247.5 

189.5 
200.9 
212.0 
223.3 
234.9 
246.8 
258.2 
270.5 

206.4 
218.8 
230.8 
243.2 
255.8 
268.7 
281.8 
294.6 

223.9 
237.4 
250  5 
263.9 
277.6 
291.6 
305.1 
319.6 

242.2 
256.7 
270.9 
285.4 
300.2 
315.3 
330.0 
345.7 

In  this  table  the  horizontal  lines  give  the  number  of  tons 
of  silage  held  by  a  silo  having  the  depth  given  at  the  left 
of  the  column. 


527.  Horizontal  Feeding  Area — In  the  construction  of 
silos  it  is  very  important  to  have  the  horizontal  dimensions 
such  that  the  rate  of  feeding  shall  be  rapid  enough  not  to 
permit  moulding  to  occur  on  the  exposed  or  feeding  sur- 
face. It  is  also  important  to  have  the  horizontal  dimensions 
as  large  as  possible  because  the  larger  the  silo  is  the  less  it 
costs  in  proportion  to  the  feed  it  stores.  Then,  too,  narrow, 
small  silos  do  not  allow  the  silage  to  settle  as  well,  and  hence 
in  them  the  necessary  losses  are  proportionally  greater 
than  in  the  larger  ones. 


426 


Rural  Architecture. 


Observations  indicate  that  if  silage  is  fed  down  at  a  rate 
slower  than  1.2  inches  daily,  moulding  is  liable  to  set  in. 
This  is  more  likely  to  be  true  in  the  upper  half  of  the  silo 
than  in  the  lower  half  but  it  will  be  prudent  to  have  the  silo 
of  such  a  diameter  as  to  lower  the  surface  more  rapidly  in 
feeding  than  is  necessary  rather  than  less  rapidly. 

A  silo  30  feet  deep  will  allow  1.5  inches  in  depth  of  silnge 
per  day  for  240  days,  and  one  24  feet  deep  will  allow  1.2 
inches  for  the  same  time.  From  the  table  on  page  424  it 
v/ill  be  seen  that  the  mean  weight  of  silage  per  cubic  foot 
for  a  silo  30  feet  deep  is  39.6  Ibs.,  and  allowing  40  Ibs.  of 
silage  per  cow  per  day  it  is  seen  that  a  cubic  foot  of  silage 
on  the  average  will  feed  a  cow  one  day.  But  from  the 
same  table  it  will  be  seen  that  if  the  silo  is  24  feet  deep 
there  will  be  required  1.114  cubic  feet  of  silage  to  give  the 
desired  weight. 

Table  giving  the  inside  diameter  of  silos  24  feet  and  30  feet  deep 
which  will  permit  the  surface  to  be  lowered  in  feeding  at  the 
mean  rate  of  1.2  to  2  inches  per  day,  assuming  40  Ibs.  of  sil- 
age to  be  fed  to  each  cow  daily. 


FEED  FOR  240  DATS. 

FEED  FOR  180  DATS. 

Silo  %lt  feet  deep. 

Silo  SO  feet  deep. 

Silo  Ufeet  deep. 

Silo  SO  feet  deep. 

No.  OP 

Cowa. 

Rate  1.2  in.  daily. 

Rate  1.5  in.  daily. 

Kate  1.6  in.  daily. 

Rate  2  in.  daily. 

Tons. 

Inside 
diameter. 

Tons. 

Inside 
diameter. 

Tons. 

Inside 
diameter. 

Tons. 

Inside 
diameter. 

10. 

48 

ft.      in. 
11       11 

48 

ft.      in. 
10         2 

36 

ft.     in, 
10         4 

36 

ft.      in. 
8        9 

15. 

72 

14         7 

72 

12         5 

34 

12         8 

54 

10        9 

20. 

96 

16       10 

96 

14         4 

72 

14         7 

72 

12         5 

25. 

120 

18        10 

120 

16         0 

90 

16         4 

90 

13       10 

30. 

144 

20         8 

144 

17         6 

108 

17       10 

108 

15         2 

33. 

188 

22          4 

168 

18       11 

126 

19         4 

126 

16         4 

40. 

192 

23        10 

192 

20         3 

144 

20         8 

144 

17         6 

45. 

'  216 

25          7 

216 

21         5 

16i 

21        11 

162 

18         7 

50. 

240 

26         8 

210 

22          7 

IfO 

23          1 

JM) 

19         7 

60. 

2S8 

29         2 

tea 

24         9 

216 

25         3 

216 

21         5 

70. 

auj 

al         6 

3H6 

26         9 

w 

27         4 

252 

23         2 

80. 

Ml 

33         8 

3M 

28         7 

288 

29         2 

'288 

24         9 

90. 

cn 

35         9 

*« 

30         4 

324 

30       11 

324 

26         3 

100. 

480 

37         8 

460 

31        11 

3CO 

32         8 

2CO 

27         8 

Danger  in  Filling  Silos.  427 

Using  these  data  the  inside  diameter  of  cylindrical  silos 
24  feet  and  30  feet  deep  which  will  hold  feed  enough  for 
different  numbers  of  cows  may  be  computed  and  such  re- 
sults are  given  in  the  preceding  table. 

528.  Danger  in  Filling  Silos. — It  never  should  be  forgot- 
ten in  connection  with  the  filling  of  silos,  that  carbon  diox- 
ide is  generated  very  rapidly  the  first  few  days  after  sil- 
age is  put  into  the  silo,  and  it  sometimes  happens  if  the 
air  is  very  still  over  night,  and  if  the  surface  of 
the  silage  is  a  considerable  distance  below  any  door,  that 
carbonic  acid  accumulates  in  sufficient  quantity  over  the 
silage  to  make  it  impossible  for  a  man  to  live  in  it.  Cases 
are  on  record  where  people  have  been  suffocated  by  going 
into  a  silo  under  these  conditions.  If  the  doors  in  a  silo  are 
so  close  together  that  a  man  standing  on  the  silage  will  have 
his  head  above  an  open  door  the  carbonic  acid  gas  will  flow 
out  of  the  door  and  not  accumulate  to  such  an  extent  as  to 
be  injurious. 

In  cases  where  the  silage  is  below  any  opening  far  enough 
to  leave  a  man's  head  below  the  opening  care  should  be 
taken  not  to  go  into  the  silo  in  the  morning  after  filling  has 
begun  until  after  the  machinery  has  been  started.  After  the 
silage  has  been  dropping  into  the  silo  for  a  few  minutes  it 
will  stir  the  air  up  sufficiently  to  render  it  pure  enough  for 
a  man  to  work  in  it  without  danger.  Ordinarily  the  air 
currents  outside  are  sufficiently  strong  to  prevent  the  car- 
bonic acid  from  accumulating,  but  it  should  be  kept  in 
mind  that  it  is  possible  on  still  nights  for  this  accumula- 
lation  to  take  place. 


PARM  MECHANICS. 


CHAPTEE    XX. 
PRINCIPLES  OF  DRAFT. 

If  it  were  possible  to  construct  a  perfect  road  its  length 
would  be  the  shortest  distance  between  the  places  con- 
nected, and  it  would  offer  no  resistance  to  movement  over 
it.  A  pair  of  parallel,  level,  smooth  and  rigid  steel  rails, 
well  bedded,  constitutes  the  nearest  approach  to  the  perfect 
road  yet  devised,  and  how  vastly  superior  the  steel  track  of 
the  railroad  is  to  the  best  paved  street  is  shown  by  the 
enormous  loads  moved  and  high  speed  attained  over  them. 

529.  How  the  Draft  Increases  With  the  Grade. — A  pull  of 
2,000  Ibs.  is  required  to  lift  a  ton  vertically,  but  to  simply 
move  it  horizontally  only  the  friction  of  the  carriage  and 
the  resistance  of  the  air  need  be  overcome.  The  more 
nearly  level  that  roads  are  built,  therefore,  the  heavier  and 
the  faster  may  loads  be  moved  over  them.  If  the  road- 
bed rises  one  foot  in  100  feet  it  is  said  to  have  a  one 
per  cent,  grade,  and  this  amount  of  slope  will  increase  the 
draft  one  per  cent,  of  the  weight  of  the  load  over  what  it 
would  be  on  the  same  road-bed  level.  A  two  per  cent,  grade 
rises  two  feet  in  every  100  feet  and  the  draft  is  increased 
by  it  two  per  cent,  of  the  load ;  a  ten  per  cent,  grade  rises 
ten  feet  in  every  100  feet  and  will  increase  the  draft  of  a 
ton  200  Ibs.  over  what  it  is  on  a  level  road  of  the  same  char- 
acter. The  heavier  the  loads  to  be  moved,  therefore,  the 


Influence  of  Grade  on  Draft. 


429 


more  objectionable  becomes  any  grade  in  the  road.  This 
is  why  with  all  railroads  the  heavier  their  freight  the  more 
they  overhaul  their  tracks  and  lower  the  grade. 


FiU.  200. — Apparatus  for  demonstrating  the  Influence  of  different  grades 
and  of  obstructions  on  the  draft  of  wagons  on  roads. 

530.  Experimental  Demonstration  of  Influence  of  Grade  on 
Draft. — In  Fig.  209  the  steel  bar  may  be  set  so  that  it 
represents  any  grade  from  one  to  twenty  per  cent.,  and 
by  setting  the  road-bed  at  these  different  grades  the  spring 
balance  shows  the  force  necessary  to  sustain  the  load  in 
the  several  cases.  If  the  load  with  the  carriage  is  made 
equal  to  60  Ibs.  then  the  scales  will  read  .6,  1.2,  1.8,  2.4, 
etc.,  up  to  12  Ibs.  for  the  20  per  cent,  grade.  If  now  the 


430  Farm  Mechanics. 

road-bed  is  set  for  a  10  per  cent,  grade  and  then  the  load, 
including  the  carriage,  varied  it  will  be  found  that  the 
draft  on  the  scale  will  be  always  10  per  cent,  of  the  load. 

531.  The  Mechanical  Principle  Involved  in  the  Relation  of 
Draft  to  Grade — It  is  a  general  truth  or  principle  in  over- 
coming any  resistance  or  in  doing  work  of  any  kind  that 
the  force  or  power  doing  the  work,  when  multiplied  by  the 
distance  through  which  it  moves,  is  always  equal  to  the  re- 
sistance or  work  multiplied  by  the  distance  through  which 
it  is  moved.     Stated  mathematically  the  equation  stands 

Power  X  Power  Distance  =  Weight  X  Weight  Distance 

or 
P.  X  P.  D.  =  W.  X  W.  D. 

Suppose  the  road-bed  in  Fig.  209  has  a  length  of  100 
and  the  grade  is  10  per  cent.,  then  if  a  load  of  60  is  drawn 
along  the  length  of  the  road  the  power  will  have  passed 
over  a  distance  of  100,  acting  parallel  with  the  road-bed, 
but,  leaving  friction  out  of  consideration,  the  work  done  is 
to  lift  the  load  vertically  through  a.  distance  of  only  10, 
and  since  the  distance  which  the  weight  is  raised  is  only 
i^of  that  over  which  the  power  has  acted  it  is  only  neces- 
sary that  the  power  shall  be  A  of  the  weight  or 

P.  X  P.  D.  =  W.  X  W.  D. 

P.  X  100  =  60  X10 
whence  100  P.  =  600 
and  Power  =  6  Ibs. 

532.  The  Steepest  Grade  Admissible — When  it  is  asked 
what  is  the  steepest  grade  which  should  be  permitted  on  a 
given  road  there  are  many  factors  which  must  be  consid- 
ered, but  the  most  general  rule  is  to  make  the  grade  as  small 
as  practicable  on  roads  where  horses  are  expected  to  carry 
all  they  can  well  handle  on  good,  nearly  level  roads,  and 


Influence  of  Grade  on  Draft.  431 

the  better  the  level  part  of  the  road,  the  longer  the  haul 
and  the  more  teams  to  pass  over  it,  the  less  steep  should  the 
grade  be.  On  all  well  designed  roads  a  great  effort  is 
usually  made  to  keep  below  a  rise  of  seven  feet  in  100  feet. 

Just  why  low  grades  are  so  necessary  will  be  readily 
understood  from  the  following  considerations  : 

About  the  maximum  walking  draft  of  a  horse  on  a  good 
level  road  is  measured  by  one-half  his  weight.  Trials  have 
shown  that  a  1,634-lb.  horse  can  exert  a  steady  pull  of 
800  Ibs.  while  walking  100  feet,  and  that  an  836-lb.  horse 
may  maintain  through  the  same  distance  a  steady  draft  of 
400  Ibs.  It  would  not  be  safe,  however,  to  repeat  such 
strains  often  nor  maintain  them  long.  Even  a  draft  equal 
to  one-fourth  the  weight  of  the  animal  is  a  heavy  and  ex- 
haustive pull.  Indeed  a  steady  pull  equal  to  one-tenth  of 
the  weight  of  the  horse  for  a  ten-hour  daily  service  at  the 
walking  pace  of  2.5  miles  per  hour  is  an  average  of  effect- 
ive service  and  the  work  of  a  1,000-pound  horse  would 
equal 


_2TT  p 


60X33,000 


Taking  this  as  the  safe  rate  of  work  for  a  team  on  the 
road  an  800-pound  horse  may  pull  steadily  80  Ibs.  ;  he  may 
pull  over  hills  at  the  rate  of  200  Ibs.  and  in  emergencies 
400  Ibs.  A  1,600-pound  horse  at  the  same  rating  may 
pull  steadily  160  Ibs.,  up  hills  400  Ibs.  and  in  an  emergency 
800  Ibs. 

It  has  been  found  that  to  move  a  gross  ton  over  a  good 
level  dirt  road  requires  a  traction  of  about  140  Ibs.  A 
team  of  800-pound  horses  may  therefore  come  to  a  hill  with 
a  load  of 

160 

r-Tjr  tons  =  2,  285f  pounds. 

•LiU 

Up  how  steep  a  grade  may  such  a  team  carry  this  load 
with  a  steady  exertion  of  200  Ibs.  per  horse?  To  over- 


432  Farm  Mechanics. 

come  the  resistance  the  road-bed  offers  to  the  load  requires 
a  steady  pull  of 


and  this  leaves  the  reserve  draft  to  go  up  the  grade 
(200  X  2)  —160  =  240 

The  load  to  be  carried  up  the  grade  is  the  weight  of  the 
team  plus  that  of  the  load  or 

(800  X  2)  +  2,  285f  =  3,  885f  Ibs. 

Up  how  steep  a  grade  will  240  Ibs.  carry  3,  8851  Ibs.? 
Solving  this  problem  by  applying  the  principle  of  (531) 
we  shall  have 

P.  X  P.  D.  =  W.  X  W.  D. 
or    240  X  100  =  3,  885f  X  W.  D. 

t\A   000 

whence    W.  D.  =  -^  =  6.176    or 

Oj    OOOrj.- 

a  rise  of  about  6.2  feet  per  100  feet,  which  is  a  6.2  per  cent. 
grade. 

By  taxing  the  team  to  its  utmost  capacity  its  effective 
power  to  ascend  the  grade  would  be 

(400  X  2)  —  160  =  640  Ibs. 
Proceeding  as  in  the  other  case  we  shall  have 

P.  X  P.  D.  =  W.  X  W.  D. 
and    640  X  100  =  3,  885f  X  W.  D. 


whence    W.  D.  =  =  16-47 


or  about  a  16.5  per  cent,  grade.     That  is,  a  grade  of  16.5 
feet  in  100  feet  is  the  steepest  dirt  road  a  team  can  be  ex- 


Influence  of  Grade  on  Draft.  433 

pected  to  carry  the  load  over  which  it  was  able  to  bring 
over  a  level  dirt  road  to  it. 

These  results  have  been  computed  from  the  standpoint 
of  an  800-pound  horse,  but  since  the  ability  of  a  team  to 
work  is  in  a  general  way  proportional  to  its  weight  the 
same  results  would  have  obtained  had  we  taken  the  1,600- 
pound  horse  with  a  proportional  load. 

533.  Good  Roads  Make  High  Grades  More  Objectionable.  — 

When  the  good  macadam  road-bed  is  substituted  for  the 
common  dirt  road  then  the  same  draft,  140  pounds,  which 
draws  a  ton  on  the  dirt  road  will  draw 

140 

-?--  =  2J  times  as  much  or  4,  666|  Ibs.  =  2£  tons. 

on  the  level  macadam  road.  Since  it  requires  but  60  Ibs. 
to  move  a  ton  on  a  macadam  road  the  team  may  come  to 
the  hill  with  a  load  of 

1RO 

~  =  2f  tons  =  6,9331  iba. 

\J\) 

The  effective  power  of  the  team  will  be 
400  —  160  =  240  Ibs. 

Up  how  steep  a  grade  will  240  Ibs.  carry  the  team  and 
2f  tons?  Solving  this  as  we  did  the  other  we  get 

240  X  100  =  6,9331  X  W.  D. 

94  000 
whence  W.  D.  =  =  3.46 


or  a  little  less  than  a  3.5  per  cent,  grade.  That  is  to  say, 
when  a  dirt  road  is  improved  so  as  to  reduce  the  draft  from 
140  Ibs.  per  ton  to  60  Ibs.  per  ton  then,  in  order  to  utilize 
this  improved  road  with  equal  effectiveness  under  the  con- 
ditions assumed,  the  6.2  percent,  grade  should  be  reduced 
to  4  per  cent.  ;  and  the  highest  grade  could  not  exceed 
9.23  per  cent. 


434  Farm  Mechanics. 


DKAFT  OF  W4GONS  ON  THE  LEVEL. 

There  are  many  factors  which  modify  the  draft  of  a 
wagon  over  a  level  road  and  some  of  the  most  important  of 
these  are : 

1.  Smoothness  of  the  road-bed. 

2.  Rigidity  of  the  road-bed. 

3.  Width  of  the  tire. 

4.  Diameter  of  the  wheel. 

5.  Distribution  of  the  load  on  the^carriage. 

6.  Direction  of  the  line  of  draft. 

7.  Rigidity  of  the  carriage. 

534.  The  Smoothness  of  the  Road-bed. — When  the  road- 
bed is  not  smooth  and  has  numerous  ruts,  stones  or  other 
obstructions  upon  its  surface,  the  draft  of  the  load  is  in- 
creased and  the  wear  on  the  vehicle  and  on  the  road-bed 
is  also  greater  so  that  much  effort  and  care  should  be  ex- 
ercised to  have  the  road  smooth.       The  increase  in  the 
mean  draft  of  the  load  is  not  so  great,  however,  as  the  other 
difficulties  which  result  for  the  reason  that  when  the  wheel 
enters  a  rut  or  passes  down  off  from  an  obstruction  there 
is  a  push  forward  which  tends  always  to  give  back  a  portion 
of  the  energy  expended  in  raising  the  load  upon  the  ob- 
struction or  out  of  the  rut. 

535.  Rigidity  of  the  Road-bed. — A  yielding  road-bed  ia 
perhaps  the  most  serious  defect  of  roads,  and  the  one  which 
increases  the  draft  more  than  any  other.     If  a  wheel  is 
steadily  cutting  into  its  road-bed  it  is  continually  tending 
to  rise  over  an  obstruction  or  out  of  a  rut,  or  it  is  doing 
what  is  in  effect  all  the  time  passing  up  a  grade,  as  repre- 
sented in  Fig.  210,  the  hill  being  steeper  in  proportion  as 
the  wheels  are  smaller. 

In  Fig.  209  is  represented  a  method  of  measuring  the  in- 
crease in  draft  due  to  the  wheel  rising  over  an  obstruction 
who'se  hight  is  a  stated  per  cent,  of  the  radius  of  the  wheel. 


Draft  of  Wagons. 


435 


The  arrangement  at  C  is  provided  with  a  screw  and  gradu- 
ated so  that  the  block  may  be  raised  or  lowered  at  will, 
setting  it  so  as  to  represent  the  wheel  passing  over  an  ob- 
struction, 3,  4,  5,  etc.,  per  cent,  of  the  radius  of  the  wheel. 
By  setting  the  road-bed  inclined  as  shown  in  the  figure,  the 
draft  is  first  noted  and  then  the  thumb  screw  at  D  is  turned 
until  the  wheel  rises  upon  the  block  and  the  difference  be- 
tween the  two  readings  of  the  scale  expresses  the  increased 
draft  due  to  the  obstruction. 


FIG.  210. 

When  the  obstruction  is  only  four  per  cent,  of  the  radius 
of  the  wheel  the  draft  is  increased  more  than  two-fold. 
That  is  to  say,  if  a  wheel  is  48  inches  in  diameter,  an  ob- 
struction of  four  per  cent,  would  be  only  .96  of  an  inch, 
and  yet  the  draft  is  made  by  it  more  than  twice  as  heavy. 

When  the  wheel  cuts  in  one  inch  the  draft  would  not  in- 
crease quite  so  much  because  the  wheel  never  rises  quite 
out  of  the  rut,  but  the  difference  between  the  draft  on  the 
macadam  and  dirt  road  is  due  mostly  to  the  difference  in 
the  yielding,  or  cutting  in  of  the  wheels. 

An  experiment  conducted  by  the  United  States  Depart- 
ment of  Agriculture,  testing  the  draft  of  ordinary  wagons 
on  a  steel  wagon  road,  showed  that  a  single  small  horse 


43 G  Farm  Mechanics. 

easily  drew  11  tons,  or  22  times  the  weight  of  the- animal, 
and  it  is  stated  in  the  report  that  the  horse  could  readily 
have  hauled  50  times  his  own  weight.  This  would  be,  for  a 
1,000-pound  horse,  25  tons,  but  of  course  with  such  a  load 
the  road  must  be  practically  level,  for  a  grade  of  one  per 
cent,  would  increase  its  draft  500  pounds. 

536.  Draft  of  Wagon  Shown  by  English  Trials The 

power  required  to  draw  a  four-wheeled  wagon  over  roads 
of  different  characters  has  been  tested  and  the  following 
expresses  the  results  in  pounds  per  2,000  Ibs.  of  gross  load: 

On  cubical  block  pavement 28  to    44  Ibs.  per  ton 

On  macadam  road 55  to    67  Ibs.  p(  r  ton 

On  gravel  road 75  to  140  Ibs.  per  ton 

On  plank  road 25  to    44  Ibs.  per  ton 

On  common  dirt  road 75  to  224  Ibs.  per  ton 

537.  Draft  With  Different  Widths  of  Tire — Prof.  J.  H. 
Waters1  has  made  an  extended  series  of  trials  to  test  the 
effect  of  the  width  of  tires  on  the  draft  of  loads  under  dif- 
ferent conditions  of  road.     He  used  always  a  net  load  of 
one  ton,  but  the  6-inch  tired  wagon  was  245  pounds  haavier 
than. the  1.5  inch,  making  the  gross  loads  3,225  and  2,980 
pounds  respectively,  when  the  wagons  were  free  from  mud. 
The  following  are  his  results: 

On  macadam  streets,  wide  tire  26  per  cent,  less  than  narrow  tire. 

On  gravel  road,  wide  tire  24.1  per  cent,  less  than  narrow  tire. 

On  dirt  roads,  dry,  smooth,  free  from  dust,  wide  tire  26.8  per  cent, 
less  than  narrow  tire. 

On  clay  road,  with  mud  deep,  and  drying  on  top  and  spongy  beneath, 
wide  tire  52  to  61  per  cent,  less  than  narrow  tire. 

On  meadow,  pasture,  stubble,  corn  ground  and  plowed  ground 
from  dry  to  wet,  wide  tire  17  to  120  per  cent,  less  than  narrow  tire. 

On  the  other  hand  he  found  that  when  the  roads  were 
covered  with  a  deep  dust,  or  with  a  thin  mud  but  hard  be- 
low, the  narrow  tired  wagon  gave  the  lightest  draft.  Also 
when  the  mud  was  thick  and  so  sticky  as  to  roll  up  on  the 
wheel,  loading  it  down,  and  again  when  narrow  tired 
wagons  had  made  deep  ruts  in  the  road  which  the  wide 

iBull.  No.  39,  Missouri  Agr.  Exp.  Station. 


Draft  of  Wagons. 


437 


wagon 


tired  wagon  tended  to  fill  up,  the  narrow  wheeled 
gave  the  lightest  draft. 

538.  Size  of  the  Carriage  Wheel — It  is  plain  from  what 
has  been  said,  that  on  yielding  road-beds  the  draft  must 
necessarily  be  heavier,  other  things  being  the  same,  the 
smaller  the  wheels  of  the  vehicle.  This  must  be  so  both 
because  small  wheels  present  less  surface  to  the  road-bed 
to  sustain  the  load,  and  because  when  the  wheel  has  de- 
pressed the  surface  it  must  move  its  load  up  a  steeper  grade 
than  the  large  wheel.  It  follows  also  from  these  state- 
ments that  wagons  with  small  wheels  must  be  more  de- 
structive to  the  road  itself,  whether  this  be  of  dirt,  gravel, 
stone  or  iron. 

Some  unpublished  data  bearing  upon  this  point  are  given 
here  by  permission  of  Prof.  T.  J.  Mairs  of  the  Agr.  Exp. 
Staflon,  Columbia,  Mo. 

Wagons  with  three  sizes  of  wheels  were  used  in  these 
experiments : 

1.  High,  44  inch  front  wheels  and  56  inch  hind  wheels. 

2.  Medium,  36  inch  front  wheels  and  40  inch  hind  wheels. 

3.  Low,  24  inch  front  whesls  and  28  inch  hin  J  wheels,  all  having 
tires  6  inches  wide. 

The  total  load  including  the  wagon  was :  For  1,  3,T62 ; 
for  2,  3,580,  and  for  3,  3,362  pounds. 

The  drafts  in  his  trials  are  stated  in  the  table  below : 


Description  of  Conditions. 

High 
wheels. 

Medium 
wheels. 

Low 
wheels. 

Dry  gravel  road;  sand  1  inch  deep;  some  small, 
loose  stones  

Lbs  per 
ton. 

34.48 

Lbs.  per 
ton. 

90.45 

Lbs.  per 
ton. 

110.2 

Gravel  road  up  grade  1  in  44  ;  covered  with  one-half 
inch  wet  sand  ;  frozen  beneath  

123.0 

132.1 

173  1 

Dirt  road  frozen  ;   thawing  one-half  inch  ;   rather 
rou^h  ;  mud  sticky  

100.6 

119.2 

139.1 

Timothy  and  blue  grass  sod,  dry,  grass  cut  

131.9 

145.2 

178  8 

Timothy  and  blue  grass  sod,  wet  and  spongy  

172.9 

202  6 

281.1 

Cornfield,  flat  culture,  with  spring-tooth  cultiva- 

178  5 

201  2 

265  ' 

Plowed  ground  not  harrowed,  dry  and  cloddy  

252.5 

302.8 

373.6 

.28 


438 


Farm  Mechanics. 


For  use  on  the  farm  the  advantage  of  truck  or  low  wheels 
comes  in  the  saving  of  labor  in  high  lifts  in  placing 
manure  and  other  materials  upon  the  wagon,  and  here  a 
sacrifice  of  strength  of  the  horse  may  advantageously  be 
made  to  save  that  of  the  man.  A  lighter  draft  and  lower 
lift  in  handling  loads  are  secured  by  using  the  low  down 
carriage  bed  in  the  upper  part  of  Fig.  211,  than  are  possi- 
ble with  the  very  low  wheeled  wagons  shown  in  the  same 
cut. 


539.  Distribution  of  Load  on  the  Carriage. — When  there 
is  nothing  to  prevent  doing  so,  the  load  carried  by  the 
wagon  should  be  so  distributed  upon  the  wheels  as  to  be  di- 
vided proportionately  to  the  surface  the  wheels  present  to 
the  ground,  and  when  the  front  wheels  are  smaller  they 
should  carry  a  smaller  load.  When  care  is  not  exercised 


FIG.  211. 


in  this  matter  there  is  danger,  especially  on  soft  roads  and 
in  the  field  generally,  of  very  materially  increasing  the 
labor  of  hauling.  When  the  load  is  heaviest  on  one  side 
the  wheels  of  that  side  are  unduly  depressed,  thus  increas- 
ing the  draft.  The  tilting  of  the  wagon  in  this  way  throws 


Draft  of  Wagons. 


43< 


the  center  of  the  load  to  one  side  still  further  and  to  a 
very  serious  degree  if  the  load  is  high,  as  is  the  case  in 
hauling  hay  or  cord-wood. 

540.  Heaviest  Load  on  the  Hind  Wheels. — In  loading  the 
ordinary  wagon  the  heaviest  load  should  be  placed  on  the 
hind  wheels  for  three  important  reasons:  First,  because 
they  are  larger  and  will  not  depress  the  road-bed  so  much 
and  will  draw  easier  if  they  do;  second,  when  the  wheels 
track,  the  front  wheels  make  a  road,  by  firming  the  ground, 
over  which  the  balance  of  the  load  may  be  more  easily- 
drawn;  third,  when  the  axle  of  the  front  wheel  is  free  to 
be  turned,  as  in  the  common  wagon,  the  slight  inequalities 
of  the  road-bed  tend  all  the  time  to  keep  the  tongue  vibrat- 
ing, so  that  there  is  a  strong  tendency,  by  this  to  and  fro 
swinging,  to  cause  the  front  wheels  to  cut  more  deeply  into 
the  ground  and  thus  increase  the  draft.  On  a  very  rigid 
road-bed  this  matter  is  not  as  important  as  in  doing  field 
work,  but  the  differences  are  large  enough  on  earth  roads 
so  that  they  should  never  be  overlooked. 

In  the  following  table  some  observed  differences  are  re- 
corded : 


Dry  sheep 
pasture. 

Dry 
meadow. 

Lbs.  per  ton. 
110.4 

Lbs.  per  ton. 
174.0 

120.0 

187.5 

129.3 

229.9 

101  8 

190  9 

These  statements  may  appear  to  contradict  the  common 
practice  of  hauling  logs  butt  end  forward  and  the  general 
tendency  of  placing  the  heaviest  portion  of  the  load  for- 
ward. The  conditions,  however,  are  quite  different  from 
those  where  there  is  a  real  advantage  in  placing  the  heav- 
iest load  forward.  The  reason  for  this  will  be  better  un- 
derstood from  the  considerations  of  the  next  paragraph. 


440 


Farm  Mechanics. 


541.  Direction  of  the  Line  of  Draft. — In  drawing  a  load 
over  a  plane  surface  which  remains  unchanged  during  the 
movement  the  least  draft  is  required  when  the  line  of  draft 
is  maintained  parallel  with  the  road  as  shown  at  A.  B., 
Fig.  212,  where  the  apparatus  may  be  used  to  clearly  dem- 
onstrate this  principle.  It  will  be  seen  that  as  the  spring 
balance  is  moved  up  upon  its  arc  the  line  of  draft  is  such 
that  it  tends  partly  to  lift  the  load  off  the  road  and  so 
much  that  if  it  were  pushed  around  until  the  direction 


t'io.  212.— Apparatus  for  demonstrating  tlie  influence  of  tlie  direuuuii  oi 
"  the  line  of  draft  on  the  draft  of  wagons. 

became  vertical  the  whole  weight  of  the  load  would  come 
upon  the  spring  balance.  Then,  too,  if  the  line  of  draft 
is  carried  below  a  parallel  to  the  road-bed  the  draft  must 
increase  because  then  it  is  partly  downward  upon  the  bed, 
tending  to  practically  increase  the  weight  of  the  load  by 
the  lost  portion  of  the  force  of  traction,  for  it  is  clear  that 
were  the  scales  carried  downward  until  the  draft  became 
vertical  to  the  road  the  whole  effect  would  be  lost  in  pro- 
ducing pressure. 

In  the  movement  of  cars  by  the  locomotive    ove,r    the 


Draft  of  Wagons. 


441 


smooth  unyielding  bed  of  the  steel. rail  the  line  of  draft 
is  always  parallel  with  the  rail. 

542.  Line  of  Draft  on  E,oad  Wagon. — The  statements  of 
the  last  paragraph  may  appear  to  be  contradicted  by  the 
general  practice  of  having  the  traces  nearly  always  slope 
decidedly  backward  and  downward.  The  former  state- 
ments, however,  are  not  incorrect,  neither  is  the  common 
practice  fundamentally  wrong.  The  apparent  contradic- 
tion grows  out  of  the  fact  that  the  road  is  seldom  either 
smooth  or  rigid  so  that  the  wheels  on  the  average  are  in 
effect  continually  rolling  up  an  inclined  plane. 

The  principle  is  clearly  shown  in  Fig.  213  where  the 
wheel  is  rising  over  the  obstruction  which  in  effect  makes 


FIG.  213.— Apparatus  for  demonstrating  the  Influence,  upon  the  draft,  of 
the  direction  of  the  line  of  the  draft  of  a  wagon  when  the  wheels  are 
passing  over  an  obstruction  or  cutting  into  the  road  or  ground. 

an  inclined  road  upon  the  general  road-bed.  If  now 
the  draft  required  to  bring  this  load  upon  the  obstruc- 
tion is  measured  when  the  line  of  draft  is  parallel  with 
the  general  road-bed  and  then  the  line  of  draft  is  made 
more  and  more  slanting  until  the  direction  finally  be- 
comes parallel  with  the  secondary  road  made  by  the  ob- 


442  Farm  Mechanics. 

struction,  it  will  be  found  that  the  draft  decreases  until 
this  direction  is  reached,  but  that  passing  beyond  it  again 
increases.  In  other  words,  the  draft  is  least  when  the  di- 
rection of  the  traces  is  parallel  with  the  effective  road-bed. 

It  is  clear,  therefore,  that  in  teaming  with  wagons  on 
the  field  and  on  any  but  rigid,  smooth  roads  the  least  draft 
is  secured  when  the  traces  incline  more  or  less  downward, 
the  amount  increasing  the  more  yielding  and  the  more  un- 
even the  road. 

In  regard  to  the  division  of  the  load  between  the  front 
and  hind  wheels  it  is  clear  that  the  hind  wheels  are  drawn 
by  the  reach  from  the  king-bolt,  the  line  of  draft  being 
nearly  horizontal,  and,  this  being  true,  it  may  fairly  be 
concluded  that  on  ordinary  roads  and  upcn  the  field  the 
load  must  draw  harder  if  the  heaviest  portion  is  not  placed 
upon  the  front  wheels  where  the  line  of  draft  can  be  more 
inclined.  It  is  quite  possible  and  even  probable  that  when 
the  unevenness  of  the  road  is  considerable  the  least  draft 
may  be  secured  when  the  front  wheels  are  carrying  more 
than  half  the  load.  More  observations,  however,  are  re- 
quired along  this  line  to  establish  the  whole  truth. 

543.  Kigidity  of  the  Carriage. — Where  the  road  is  not  per- 
fectly smooth  and  where  the  speed  is  faster  than  a  medium 
walk,  springs  under  the  load  diminish  the  draft  and  the  ad- 
vantage of  elasticity  increases  with  the  roughness  of  the 
road  and  with  the  speed.  For  small  and  rigid  inequalities 
in  the  road  the  maximum  advantage  is  secured  in  the  use 
of  the  elastic  tire,  and  especially  with  the  pneumatic  form, 
where  the  load  is  not  too  heavy,  because  in  these  cases 
the  energy  which  would  be  lost  by  concussion  is  prevented, 
the  tire  quickly  and  effectually  conforming  to  the  road. 
Where  the  loads  must*  be  heavy,  and  where  the  inequalities 
are  larger,  then  springs  under  the  load  carried  by  the  axles 
respond  in  rapid  transit  and  relieve  the  concussions  and 
thus  lessen  the  draft,  diminish  the  strain  upon  the  car- 
riage, and  permit  less  injury  to  the  road. 


Draft  of  Wagons.  443 

544.  Results  of  General  Morin's  Experiments  in  France. — 
General  Morin,  after  a  series  of  experiments  carried  on 
under  the  French  government,  reached  the  following  con- 
clusions regarding  the  draft  of  carriages  on  roads : 

1.  The  traction  is  directly  proportional  to  the  load,  and 
inversely  proportional  to  the  diameter  of  the  wheel. 

2.  Upon  paved  or  hard  macadam  roads  the  traction  is 
independent  of  the  width  of  the  tire  when  this  exceeds 
three  or  four  inches. 

3.  At  a  walking  pace  the  traction  is  the  same  for  car- 
riages with  springs  as  for  those  without  springs. 

4.  Upon  a  macadam  or  paved  road  the  traction  increases 
with  the  speed  above  a  velocity  of  2.25  miles  per  hour. 

5.  Upon  soft  roads  of  earth  or  sand  the  traction  is  inde- 
pendent of  the  velocity. 

6.  The  destruction  of  the  road  is  in  all  cases  greater 
as  the  diameter  of  the  wheels  is  less,  and  it  is  greater  by 
the  xise  Q£  carriages  without  springs  than  of  carriages  with 
them. 


OHAPTEK  XXL 

CONSTRUCTION  AND  MAINTENANCE  OF  COUNTRY 
ROADS. 

Having  outlined  the  principles  underlying  the  draft  of 
wagons  on  roads  the  next  consideration  should  be  how  to 
make  and  maintain  the  road  for  the  given  locality  which, 
everything  considered,  is  the  most  economical. 

545.  Establishing   the    Grade. — For   ordinary    country 
roads  the  road-bed  will  generally  conform  with  the  natural 
slope  of  the  surface  over  which  it  passes ;  steep  hills,  how- 
ever, should,  if  possible,  always  be  avoided  either  by  turn- 
ing to  one  side  or  by  grading  and  filling. 

Where  the  hills  are  short  and  steep  they  may  usually  be 
graded  down  to  better  advantage  than  to  pass  around  them, 
but  when  the  hill  is  both  long  and  high  then  it  may  be  best 
to  reduce  the  grade  by  passing  obliquely  up  the  hill,  or  in 
mountainous  countries  where  ranges  are  crossed  through 
passes  it  often  becomes  necessary  to  pass  down  the  long 
steep  slopes  by  a  series  of  zigzags,  having  short  and  steep 
rounded  turns. 

546.  Factors  to  Be  Considered  in  Establishing  the  Grade.— 
There  are  many  factors  which  must  be  considered  in  de- 
ciding the  particular  grade  a  road  over  a  given  hill  may 
be  permitted  to  have.       If  the  road  for  the  main  travel  is 
generally  excellent  and  level,  with  a  good   deal  of  traffic 
over  it,  then  it  is  important  to  keep  the  grade  as  low  as 
practicable.       Where  the  country  is  generally  rolling,  so 
that  there  are  many  hills  which  must  in  any  event  have 
a  high  grade,  it  will  not  be  as  important  to  cut  other  hills 
down  as  much  as  a  more  level  country  would  warrant. 


Eoad  Drainage.  445 

The  better  the  more  level  portions  of  the  road  are,  where 
heavy  teaming  is  done,  the  more  important  it  is  to  reduce 
the  grade  -to  a  low  per  cent,  because  it  is  important  to  be 
able  to  go  over  any  hill  readily  which  can  be  approached 
with  the  largest  load  the  team  is  able  to  handle  without  in- 
jury to  itself.  The  great  importance  of  this  point  will  be 
readily  understood  when  it  is  stated  that  the  steepest  grade 
admissible  on  an  average  macadam  road  is  10.5  per  cent., 
and  on  a  dirt  road  in  good  condition  16  per  cent  But 
as  these  grades  will  tax  the  team  to  its  utmost  the  hills 
should  not  be  permitted  to  rise  if  practicable  faster  than 
4  feet  in  100  feet  for  the  ordinary  macadam  and  6.2  feet 
in  100  feet  for  the  earth  road  in  good  condition. 

In  thinly  settled  sections  people  must  be  content  to  im- 
prove the  roads  gradually,  but  if  the  end  finally  to  be 
reached  is  kept  in  mind  all  the  time  it  will  usually  be  pos- 
sible to  make  each  year's  work  count  as  permanent  im- 
provement and  avoid  tearing  down  one  year  the  work  of 
the  years  preceding. 


EOAD  DRAINAGE. 

The  keeping  of  the  road  dry,  both  above  and  below,  ia 
the  most  fundamental  necessity  of  a  good  permanent  high- 
way. Fill  any  soil,  however  hard  and  firm,  completely 
with  water,  and  a  child  walking  over  it  will  mire ;  and  to 
completely  drain  and  dry  any  soft  and  marshy  place  will 
leave  it  so  that  heavy  loads  may  be  moved  across  it  readily 
and  safely.  Drainage  is  one  of  the  first  requisites  of  a 
good  road. 

In  some  places  only  surface  drainage  requires  attention. 
Where  the  surface  is  more  or  less  rolling  and  underlaid 
with  coarse  porous  materials,  so  that  standing  water  in. 
the  ground  does  not  occur  within  10  to  20  feet  of  the  sur- 
face, under  drainage  will  not  be  necessary;  but  wherever 
the  adjacent  fields  would  be  improved  by  drainage,  wher- 
ever the  ground  is  springy,  and  wherever  the  ground  war 


446  Farm,  Mechanics. 

\ 

ter  at  any  season  of  the  year  rises  to  within  three  or  four 
feet  of  the  surface  there  the  road-bed  should  be  drained. 
In  humid  climates  provisions  should  be  made  to  surface 
drain  every  road. 

547.  The  Relation  of  Water  to  Koads. — When  a  soil  is 
completely  filled  with  water  the  individual  soil  grains  are 
invested  by  water  and  tend  to  float  in  it  so  that  there  is  the 
greatest  freedom  of  motion  of  the  particles.  On  the  other 
hand  let  all  water  be  removed  from  the  soil  and  the  ground, 
while  hard,  easily  frets  into  fine,  loose,  separate  dust 
particles,  which  not  only  increase  the  draft  but  are  easily 
drifted  away  by  the  wind,  thus  injuring  the  road  much 
as  it  would  be  were  the  top  washed  away  by  running 
water. 

There  is  a  medium  condition  or  amount  of  water  in  the 
soil  which  gives  it  power  to  withstand  the  eroding  tendency 
of  the  tramp  of  the  horses'  feet  and  the  rolling  of  the 
wheels.  When  sand  is  just  wet  enough  its  surface  is  hard 
and  will  carry  a  heavy  load,  the  grains  being  bound  to- 
gether by  the  surface  tension  of  the  water  films.  So,  too, 
with  the  clay  roads  and  those  of  the  best  of  loam^  the  right 
amount  of  water  always  present,  so  as  to  keep  the  sur- 
face damp  and  dark  without  making  them  soft,  greatly 
improves  the  quality  and  lengthens  their  life.  So  valua- 
ble is  the  right  amount  of  water  on  earth  roads  that  sprink- 
ling them  in  arid  and  semi-arid  climates  and  in  dry  times 
in  humid  climates,  is  one  of  the  most  effective  means  of 
maintenance. 

548.  Depth  of  Under  Drainage. — Where  under  drainage  is 
needed  the  drain  should  not  be  less  than  three  to  four  feet 
deep,  and  this  is  especially  true  if  heavy  traffic  is  to  be 
maintained  over  it. 

No  one  thinks  of  walking  on  the  yielding  surface  of  the 
water  of  a  lake  or  stream,  but  let  it  be  covered  with  a  suffi- 
ciently thick  layer  of  ice  and  it  then  makes  the  best  kind  of 
a  road-bed.  The  drained  ground  beneath  the  road  surface 


Road  Drainage.  447 

must  be  sufficiently  thick  to  float,  on  the  soft  soil  beneath, 
any  load  which  may  be  driven  along  it,  just  as  the  ice  floats 
its  burden. 

549.  Place  For  the  Drain — In  the  narrow  roads  of  eight 
to  sixteen  feet,  where  the  water  to  be  removed  is  that  which 
may  be  raised  by  hydrostatic  pressure  vertically  upward 
beneath  the  road-bed,  the  best  place  for  the  drain  is  di- 
rectly beneath  the  center  of  the  drive-way. 

Where  the  main  source  of  the  water  causing  the  trouble 
is  an  underflow  through  sands  and  gravels  from  adjacent 
higher  lands  then  the  drain  should  be  placed  upon  the  side 
of  the  road  from  which  the  water  comes. 

Where  the  ground  is  marshy  on  all  sides,  and  particu- 
larly if  the  road  is  wide,  it  may  then  be  necessary  to  lay 
two  lines  of  tile,  one  on  each  side. 

If  springy  places  occur  under  or  near  the  road-bed 
drains  must  be  connected  with  the  spring  itself,  so  as  to 
effectually  remove  the  excess  of  water. 

550.  Fall  of  the  Drain.— The  fall  of  the  drain  will  usu- 
ally conform  somewhat  nearly  to  the  grade  of  the  road-bed, 
but  should  not  be  less  than  two  inches  in  100  feet,  if  this 
can  be  secured.  It  will,  however,  be  necessary  sometimes  to 
lay  the  drain  on  a  slope  less  than  this,  even  as  low  as  -J 
an  inch  in  100  feet.     In  all  cases  care  should  be  exercised 
to  lay  the  tile  on  a  true  grade,  not  allowing  them  to  drop 
anywhere  below  or  rise  above  a  rigidly  maintained  grade 
line.     If  they  are  not  laid  in   this    manner   water    will 
stand  in  the  sags  and  behind  the  bends,  and  in  these  places 
the  tile  may  become  filled  with  silt. 

It  may  sometimes  occur  that  the  road  is  so  nearly  level 
that  there  is  no  fall  for  the  drain.  In  such  cases  it  may 
be  necessary  to  lay  the  beginning  end  of  the  drain  nearer 
the  surface  of  the  ground  by  as  much  as  six  or  even  twelve 
inches.  In  this  way  there  could  be  given  a  fall  of  one  inch 
in  100  feet  over  a  distance  of  1,200  feet,  but  of  course 


448  Farm  Mechanics. 

the  upper  portion  of  the  road  could  not  be  as  well  drained 
and  the  plan  should  be  followed  only  where  there  is  no 
other  alternative. 

551.  Outlet  of  the  Drain. — The  drain  should  be  turned 
out  to  the  side  of  the  road  whenever  there  is  an  opportunity 
for  doing  so,  that  is,  whenever  there  is  a  natural  line  of 
drainage  leading  across  the  road  which  will  answer  for  the 
purpose.     The  free  end  of  the  drain  is  best  made  of  one 
length  of  cast  iron  sewer  pipe  eight  feet  long,  because  this 
will  not  be  injured  by  freezing  nor  be  easily  broken.  There 
should.be  a  free  fall  at  the  end  of  the  drain,  and  it  is  better 
that  the  opening  should  be  protected  by  some  sort  of  metal 
grating  or  screen  to  prevent  animals  from  running  in  in 
dry  times. 

* 

552.  Size  of  Tile. — Tile  three  inches  in  diameter  is  the 
best  to  use  for  ihe  reason  that,  in  case  the  grade  is  very 
small,  slight  errors -in  laying  the  line  cannot  carry  the  en- 
tire opening  of  the  tile  above  or  below  the  grade  line  and 
hence  permit  the  drain  to  be  entirely  closed  by  silt. 

553.  Kind  of  Tile — Where  the  tile  can  be  laid  two  feet 
or  more  below  the  surface  of  the  road  ordinary  drain  tile 
which  are  well  burned,  straight,  smooth  inside  and  having 
the  ends  cut  squarely  off  so  that  they  may  fit  closely  to- 
gether are  best.     Great  care  should  be  taken  in  placing  the 
tile  to  turn  them  until  the  ends  fit  very  closely  all  the  way 
around,  and  then  to  fix  them  rigidly  there.     This  care  is 
needed  in  order  to  prevent  silt  from  being  washed  in  at 
the  joints. 

Where  the  tile  must  come  less  than  two  feet  below  the 
surface  it  will  be  safer  either  to  use  the  vitrified  drain  tile 
or  else  second  quality  sewer  tile  not  likely  to  be  disinte- 
grated by  frost. 

554.  Surface  Drainage — The   quick   removal   of  water 
from  the  surface  of  a  road  and  the  prevention  of  seepage 


Eoad  Drainage.  449 

down  through  the  road-bed  are  the  most  important  points  to 
be  secured  in  the  matter  of  maintenance.  The  surface  of 
every  road,  therefore,  should  be  so  shaped  as  to  act  like 
a  roof  in  throwing  all  rains  quickly  and  completely  off, 
permitting  only  a  little  moisture  to  be  drawn  downward  by 
capillary  attraction  to  moisten  the  material  and  lessen 
the  formation  of  dust.  If  the  compacted  material  of  the 
road  and  the  road-bed  beneath  it  can  be  kept  with  only  a 
small  per  cent,  of  capillary  water  in  them  the  danger  of 
injury  from  frost  is  greatly  lessened  and  the  liability  to 
soften  during  wet  periods  is  also  largely  removed. 

Water  should  under  no  conditions  be  permitted  to  stand 
either  upon  the  surface  nor  along  the  side  of  the  road,  the 
shape  being  sufficiently  rounded  to  throw  the  rains  quickly 
to  either  side,  and  the  surface  ditches  deep  enough,  clean 
enough  and  possessing  sufficient  capacity  to  carry  all  water 
rapidly  away*  -  . 

555.  Slope  of  the  Eoad  Surface. — [n  order  to  have  quick, 
complete  surface  drainage  it  is  necessary  to  so  arch  the 
face  as  to  make  a  road  twelve  feet  wide  three  inches  higher 
,in  the  center  than  at  either  margin,  a  slope  of  about  four 
per  cent,  or  four  inches  in  100  inches.       But  if  the  road 
has  itself  a  considerable  grade,  then  the   slope    must    be 
made  enough  greater  than  four  per  cent,  to  force  the  water 
to  the  side  ditches  rather  than  to  permit  it  to  flow  down 
the  center  of  the  road.       But  evenness  or  smoothness  of 
surface  is  the  most  important  condition  to  be  secured  and 
maintained  in  order  to  afford  perfect  drainage.       If  the 
road  surface  is  left  uneven,  or  is  permitted  to  become  so, 
no  amount  of  slope  which  can  be  tolerated  will  secure  the 
drainage. 

The  road  must  not  be  made  too  rounding  or  sloping  for 
the  reason  that  then  teams  all  drive  in  one  place  on  the 
surface  and  wear  it  into  ruts  and  this  prevents  drainage. 

556.  Water-Breaks. — On  steep  grades  where  the  hill  is 
long  it  is  a  common  practice  to  throw  a  ridge  obliquely 


450  'Farm  Mechanics. 

across  the  road  at  intervals  to  turn  the  water  to  the  side. 
This  is  a  bad  practice  and  should  be  avoided  wherever 
possible,  and  in  all  but  the  steepest  grades  this  may  be  done 
by  making  the  slope  of  the  road  higher  than  the  grade. 

If  the  water  cannot  be  turned  off  in  this  way  it  is  bet- 
ter to  make  two  paved  gutters  meeting  V-shaped  in  the  cen- 
ter of  the  road  with  the  point  up  the  grade.  The  paving  will 
prevent  washing  and  making  the  gutters  meet  in  the  cen- 
ter does  not  tip  the  wagon  in  passing  across  them. 

Whenever  it  becomes  necessary  to  carry  water  across 
a  road  on  a  hill  from  one  gutter  to  the  other  it  is  much 
better  to  carry  it  under  the  road  than  above  it,  as  is  so 
often  done  with  the  aid  of  water-breaks.  A  culvert  is  of 
course  necessary  but  it  should  be  used. 


TEXTUEE  OF  ROAD  MATERIALS. 

Closeness  of  texture  is  necessary  to  the  building  of  a 
solid  road.  The  more  completely  all  pores  can  be  obliter- 
ated and  the  road  given  the  close  texture  of  iron  the  better 
and  more  durable  will  it  be. 

Field  soil  in  its  natural  condition  may  have  from  30 
to  50  per  cent,  of  space  unoccupied  by  anything  but  water 
and  air,  and  in  this  condition  it  cannot  form  a  good  road. 
It  is  too  yielding  to  pressure  and  water  percolates  through 
it  too  rapidly.  When  it  is  properly  rolled  and  tamped 
the  pore  space  is  very  greatly  reduced,  giving  it  so  close 
a  texture  that  water  does  not  enter  it  readily,  and  so  large 
a  portion  of  the  grains  are  in  actual  contact  that  it  ap- 
proaches the  character  of  a  rock.  Of  whatever  material  a 
road  is  built  it  should  permit  the  parts  to  pack  so  closely  as 
to  resemble  a  solid  rock. 

557.  Hoads  Should  Be  Built  in  Layers. — Whether  a  road 
is  to  be  built  of  crushed  rock  or  earth  it  is  indispensable 
that  the  materials  used  shall  be  put  on  in  layers.  The 
thickness  of  the  layers  will  depend  primarily  upon  the 


Texture  of  Road  Materials.  451 

size  of  the  pieces  of  material  used,  the  layers  being  thicker 
the  coarser  the  material.  With  crushed  rock  having 
pieces  2  to  2  1-2  inches  in  diameter  the  layers  will  need  to 
be  3  to  4  inches  thick ;  with  smaller  pieces  the  layers  should 
be  thinner.  If  thicker  layers  than  these  are  made  the  ef- 
fect will  be  the  formation  of  a  closely  packed  crust,  a  lit- 
tle thicker  than  the  diameter  of  the  material  used,  over  a 
loose  and  open  structure  below. 

The  hardest  and  best  earth  road  can  be  built  only  by 
spreading  the  material  on  very  uniformly  in  thin  layers 
and  thoroughly  compacting  each  layer  before  the  next  is 
put  in  place;  the  thickness  of  these  layers  should  be  2 
inches  and  less,  rather  than  more. 

558.  Uniformity  of  Size  of  Material  Used. — It  is  impossi- 
ble to  crush  rock  into  sizes  varying  all  the  way  from  fine 
dust  to  pieces  1.5  inches  in  diameter  and  then  use  this  ma- 
terial unsorted  to  make  a  solid,  unyielding  road.       The 
materials  when  laid  down  at  once  with  all  sizes  mixed  will 
not  pack  so  as  not  to  work  up  loose  with  the  travel  upon  it ; 
and  this  is  the  main  reason  why  more  solid  roads  cannot 
be  built  from  earth. 

Crushed  rock  must  be  carefully  separated  into  nearly 
uniform  sizes  by  means  of  screens  and  the  different  grades 
applied  to  the  road  in  layers. 

When  a  layer  is  made  of  only  a  single  size  of  pieces 
these  may  be  brought  together  by  packing  so  that  all  touch 
and  press  firmly  against  one  another.  If  now  a  grade  is 
used  of  smaller  pieces  such  as  will  work  readily  into  the 
pores  left  between  the  angles  of  the  larger  ones,  pressing 
hard  upon  all  sides,  a  still  more  stable  layer  will  be  formed. 
If  it  were  practicable  to  follow  this  method  step  by  step 
there  would  be  reproduced  a  nearly  solid  rock  from  the 
fragments  made  and  the  most  substantial  of  roads  built. 

559.  Shape  of  Fragments. — The  shape  of  the  materials 
used  in  road  building  has  important  bearings  on  the  quality 
pf  the  road.     The  best  form  is  that  which  approaches  most 


452  'Farm  'Mechanics. 

closely  to  the  cube  with  broad,  flat  faces,  sharp  angles  and 
having  the  same  diameter  in  three  directions.  Fragments 
of  this  form  pack  most  readily  and,  as  the  broad,  flat  faces 
set  against  each  other,  the  fragments  do  not  so  readily  turn 
under  the  wheel  or  horses'  feet  and  withstand  a  heavier 
load  without  crushing. 

Where  sands  and  gravels  are  used  in  road  building  those 
of  glacial  origin  which  are  much  sharper  and  more  angular 
than  water  worn  types  are  much  to  be  preferred,  for  the 
simple  reason  that  when  packed  together  they  give  a  more 
rigid  body  and  stronger  binding.  Beach  gravels  and  sands 
cannot  be  held  rigidly  by  any  ordinary  cementing  material 
because,  with  the  round,  smooth  surfaces,  there  is  little 
opportunity  for  any  locking. 

560.  Cleanness  of  Material. — Where  crushed  rock  is  used 
in  the  building  of  roads  it  is  important  that  these  materials 
be  clean  and  free  from  dirt,  clay  and  rubbish  of  any  sort. 
So  with  gravel  or  sand,  when  these  are  called  for  they 
should  be  clean.  In  general,  anything  which  works  against 
uniformity  of  material  should  be  avoided. 


EARTH  EOADS. 

In  the  country  in  most  parts  of  the  United  States  the 
greatest  number  of  miles  of  travel  for  a  long  time  to  come 
must  be  made  over  earth  roads.  It  is  therefore  of  great 
importance  that  they  should  be  built  in  the  best  possible 
manner.  The  proper  construction  of  earth  roads  is  made 
the  more  important  through  the  fact  that  when  well  built 
and  well  maintained  there  is  no  road  easier  on  the  team, 
the  carriage  or  the  parties  riding,  where  speed  is  an  im- 
portant consideration,  than  an  earth  road. 

561.  Forming  the  Road-bed. — After  the  grade  has  been 
established  and  under-drainage  provided  where  necessary, 
all  organic  material  and  stone  should  be  cleared  out  of  the 


Earth  Roads.  453 

war  and  the  road  given  the  form  and  width  desired  by  a 
road  machine  such  as  represented  in  Fig.  215,  or  by  other 
means. 

The  road  itself  should  have  a  width  of  1C  or  18  feet  bor- 
dered on  either  side  by  a  strip  of  grass  three  feet  wide,  out- 
side of  which  should  be  the  surface  drains,  where  needed, 
five  feet  wide  at  the  top,  two  feet  at  the  bottom  and  24 
inches  deep,  making  a  total  width  of  32  or  34  feet  as  rep- 
resented in  Fig.  214. 


The  center  of  the  road-bed  should  be  thoroughly  rolled 
with  as  heavy  a  roller  as  practicable  in  order  to  compact  it 
and  to  discover  in  it  any  soft  places.  If  soft  places  are 
found  these  should  be  filled  and  brought  to  the  proper 
level.  If  the  soft  place  is  due  to  a  different  kind  of  ma- 
terial this  should  be  removed  and  replaced  by  other  and 
better. 

The  center  of  the  finished  road  should  be  two  to  six 
inches  higher  than  the  margins  at  the  grass  border,  vary- 
ing with  the  width  of  the  track,  in  order  to  give  quick,  com- 
plete surface  drainage,  and  this  should  be  built  up  in  thin 
successive  layers  of  as  uniform  material  as  possible.  If 
earth  is  brought  in  from  the  sides  and  ditches  great  care 
should  be  exercised  in  distributing  it  evenly,  and  thor- 
oughly harrowing  it  ahead  of  the  roller,  so  as  to  secure  the 
necessary  uniformity  of  texture.  This  is  of  the  utmost  im- 
portance in  order  to  prevent  the  formation  of  ruts.  Thor- 
ough rolling  should  follow  the  addition  of  each  layer  of  ma- 
terial and  should  be  kept  up  until  a  hard,  even  surface  has 
been  secured. 
29 


454  Farm  Mechanics. 

In  making  earth  roads  it  is  particularly  important  not 
to  make  them  wider  than  necessary  because  the  narrow  roi>d 
is  always  more  quickly  and  better  drained  and  lack  of 
drainage  more  than  anything  else  will  destroy  the  earth 
road. 


FIG. 215. — View  of  one  type  of  road  machine, Champion  road  grader. 

If  the  soil  contains  cobble  stones  everything  larger  than 
one  inch  in  diameter  should  be  thrown  out,  otherwise  they 
will  form  ruts. 

If,  in  establishing  the  necessary  grades  on  the  earth 
roads,  fills  must  be  made,  this  filling  should  be  done  sys- 
tematically, distributing  the  earth  in  uniform  layers  which 
are  thoroughly  firmed  with  the  roller  as  the  work  pro- 
gresses. 


Earth  Roads.  455 

562.  Utilizing  the  Old  Road  as  a  Road-bed. — In  cases 
•where  the  grade  does  not  require  changing'  and  where  nat- 
ural under-drainage  is  adequate  the  old  road-bed  may  be 
utilized  in  its  already  tramped  and  packed  condition  upon 
which  to  build  the  new  road.  This  may  be  fitted  with  the 
road  machine  by  throwing  the  loose  and  uneven  portion  of 
the  surface  outward  to  form  the  shoulders.  Then  if  there 
are  still  low  places  these  should  be  filled  in  and  thoroughly 
packed  with  the  roller,  the  use  of  which  is  necessary  even 
where  no  leveling  is  needed,  in  order  to  discover  any  soft 
spots,  quite  certain  to  exist,  and  in  order  to  give  the  foun- 
dation a  more  thorough  packing  than  the  wagons  have  se- 
cured. 

563.  Preparing  the  Road-bed  a  Year  or  More  in  Advance. — 
It  will  generally  be  found  advantageous  to  get  the  road-bed 
into  proper  shape  to  receive  the  surfacing  material,  whether 
this  be  gravel  or  crushed  rock,  a  year  or  more  in  advance, 
utilizing  the  weathering  of  rains,  the  frost  of  winter  and 
the  traffic  to  settle  the  road-bed,  but  directing  and  assisting 
these  agencies  by  a  timely  and  judicious  use  of  the  harrow, 
road  machine  and  roller.  It  is  particularly  important  to 
allow  time  to  intervene  where  there  has  been  much  filling 
necessary. 

564.  Roads  on  Gravelly  Loam. — Where  the  soils  are  a 
gravelly  loam  the  best  earth  roads  are  possible.  The  reason 
for  this  is  found  in  the  fact  that  a  gravelly  loam  is  made  up 
of  large  and  small  grains  in  such  proportions  that  when 
they  are  thoroughly  worked  and  compacted  the  coarser  sand 
particles  work  in  between  the  gravel,  and  the  fine  clay  par- 
ticles between  those  of  sand,  in  such  a  way  that  there  is  left 
almost  no  open  space ;  under  these  conditions  the  water  is 
shed  the  most  rapidly  and  completely  so  that  the  road  is  less 
liable  to  soften  under  the  travel  over  it  and  it  is  less  liable 
to  be  injured  by  frost. 

565.  Roads  in  Fine  Clay  Soil. — Where  the  soil  is  a  fine  ad- 
hesive clay  it  is  hardly  possible  to  make  a  good  road  with- 


456  Farm  Mechanics. 

out  the  aid  of  foreign  material.  Of  course  by  grading  it 
into  proper  form  so  as  to  secure  the  needed  drainage  the 
road  will  be  good  when  it  is  not  wet,  and  under  these  con- 
ditions it  will  remain  fair  much  longer  than  if  not  so  pre- 
pared because,  when  this  soil  has  been  once  thoroughly  com- 
pacted and  dry,  water  enters  it  very  slowly,  so  that  it  is 
only  during  long  wet  spells  and  when  the  frost  is  going  out 
that  the  most  serious  injury*  to  the  road  comes. 

566.  Clay  Roads  Surfaced  With  Gravel. — Where  gravel  of 
suitable  quality  is  available  a  covering  of  three  or 
four  inches,  thoroughly  rolled  and  packed,  will  very  greatly 
improve  the  surface  of  a  clay  road,  preventing  it  from  soft- 
ening so  readily  with  every  rain  and  with  the  action  of 
frost.  Even  sand  and  good  loam,  where  nothing  better  is 
available,  will  improve  the  quality. 

In  some  cases  burning  the  clay  has  been  practiced  so  as 
to  render  it  less  plastic  and  sticky,  but  this  practice  will  be 
one  of  the  last  to  be  resorted  to  at  this  time  of  cheap  trans- 
portation and  high  price  of  fuel. 

587.  Sandy  Roads. — The  making  of  good  roads  in  a  coun- 
try of  very  sandy  soil  is  extremely  difficult  on  account  of 
the  nearly  complete  absence  of  binding  properties  in  the 
sand  when  dry.  If  there  were  any  cheap  method  of  keep- 
ing the  surface  wet,  sand  would  make  an  excellent  road. 
Even  the  rounded  grains  of  beach  sand  for  a  short  time 
after  the  waves  have  withdrawn  are  so  tightly  bonded  that 
a  horse  may  canter  along  the  beach,  making  but  little  im- 
pression upon  it.  The  water,  however,  drains  away  so 
rapidly  from  the  coarse  clean  rounded  grains  that  there  is 
no  longer  anything  to  bind  them  together,  and  the  foot  or 
wheel  easily  sets  them  aside.  When,  however,  there  are  a 
sufficient  number  of  much  finer  particles  commingled  with 
the  coarse  sand  grains  a  loam  is  the  result  whose  water 
holding  power  is  increased  so  that  for  a  longer  time  the 
grains  are  bonded  together  by  it,  enabling  the  loam  to  form 
the  better  road.  On  the  other  hand,  the  amount  of  water 


Earth  Roads.  457 

may  be  too  great  to  permit  it  to  act  as  a  binding  material 
and  as  the  water-holding  power  of  the  clays  is  greater  than 
the  loams,  they  more  quickly  come  into  the  condition  of 
over  saturation  during  long  rains  and  so  the  loam  which  is 
intermediate  between  the  two  extremes  makes  the  best  earth 
road,  sand  tending  most  of  the  time  to  retain  too  little 
water  and  the  clay  retaining  too  much  for  tight  binding. 

With  this  principle  to  direct  practice  it  is  clear  that  if  the 
right  amount  of  finer  soil  particles  can  be  obtained  to  in- 
corporate with  the  sand  of  sandy  roads  their  firmness  will 
be  increased.  It  is  unfortunately  too  often  true  that  in 
districts  where  sandy  roads  prevail  there  is  no  clayey  or 
loamy  material  available,  either  to  incorporate  with  the 
sand  or  to  place  above  it. 

568.  The  Use  of  Straw,  Sawdust  and  Tan  Bark  on  Sandy 
Roads. — It  is  well  known  that  these  materials  when  applied 
to  sandy  roads  have  temporarily  a  beneficial  effect.     The 
fundamental  principle  underlying  this  improvement  is  that 
stated  in  the  last  paragraph ;  that  is,  in  the  power  they 
have  of  maintaining  a  higher  per  cent,  of  water  in  the  sand, 
which  is  necessary  in  order  to  bind  the  grains  together. 
The  sawdust,  tan  bark  and  straw  act  in  two  ways  to  main- 
tain the  needed  amount  of  water  in  the  sand.     At  first 
they  act  as  a  mulch,  lessening  the  rate  of  evaporation  from 
the  surface.     Later,  when  they  begin  to  disintegrate,  they 
form  a  humus-like  material,  in  its  physical  effects,  which 
increases  the  capillary  power  and  diminishes  the  rate  of 
percolation  downward  after  rains. 

The  reason  why  these  materials  are  only  temporary  in 
their  effect  is  because  they  rapidly  decay,  being  converted 
into  soluble  salts  and  gaseous  products  which  finally  leave 
the  sand  as  if  nothing  had  been  added. 

569.  Road  Gravel. — It  occasionally  happens  that  natural 
gravel  beds  are  found  which  possess  the  right  characteris- 
tics for  making  roads,  and  when  the  gravel  is  just  right  ex- 
cellent roads  may  be  made  from  it. 


458  Farm  Mechanics. 

There  are  several  important  features  which  a  good  road 
gravel  must  possess: 

1.  There  must  be  one  prevailing  size  of  pebble  in  suffi- 
cient quantity  so  that  when  thoroughly  rolled  they  press 
against  one  another. 

2.  There  must  be  enough  of  the  finer  sizes  of  coarse  sand 
and  fine  gravel  to  fill  the  voids  between  the  coarser  gravel. 

3.  There  must  be  enough  of  fine  loam  to  fill  the  voids 
between  the  coarse  sand  and  fine  gravel  and  retain  a  suffi- 
cient amount  of  water  to  bind  the  sand  grains  together  and 
prevent  their  rolling. 

4.  The  coarse  and  fine  gravel  and  the  sand  must  be  made 
up  of  more  or  less  angular  fragments    in  order  that  flat 
faces  of  rock  may  set  together  and  thus  lessen  the  danger 
of  rolling  and  of  crushing  under  the  weight  of  the  load. 

It  is  not  possible  to  give  specific,  concise  directions  for 
identifying  a  good  road  gravel,  but  a  man  who  has  seen 
and  worked  with  it  readily  recognizes  it. 

570.  Clean  White  Gravel  Not  Suitable. — It  will  be  appar- 
ent at  once  that  the  several  characteristics  which  have  been 
pointed  out  are  not  likely  often  to  occur  together  in  just 
the  right  ratios ;  and  so  there  will  be  all  possible  gradations 
from  the  ideal  gravels  to  those  which  will  not  answer  at  all. 
Indeed  it  must  be  said  that  most  gravel  beds  have  had  the 
finer  materials  so  completely  washed  out  that  only  clean 
sand  and  gravel  remains ;  and  when  this  is  true  it  is  useless 
to  try  to  make  a  road  with  it.     Such  materials  can  only  be 
used  to  temper  a  road  which  is  too  clayey  in  its  texture, 
by  reducing  its  water  capacity. 

571.  Texture  of  Gravels  Altered  by  Crushing  and  Screen- 
ing.— It  happens  in  the  majority  of  cases  that  much  of  the 
gravel  is  too  large  and  too  rounded  to  permit  close  packing 
and  fast  binding.     When  this  is  true  much  better  qualities 
may  be  secured  by  using  either  the  crusher  or  the  screen 
oi'  both  together,  one  form  of  which  is  represented  in  Fig. 
216.     It  will  be  at  once  apparent  that  where  much  of  the 


Earth  Roads. 


459 


gravel  is  too  coarse,  to  run  it  through  the  crusher  so  as  to  re- 
duce the  material  to  a  more  uniform  size  and  at  the  same 
time  to  increase  the  angularity  of  the  fragments  will  make 
a  much  better  road  material  to  use  either  by  itself  or  as  a 
tempering  material. 


FIG.  216. —  Champion  rock  crusher  and  screen. 

572.  Some  Gravels  Contain  Too  Much  Clay. — There  are 
many  deposits  of  gravelly  clay  which  it  might  appear  would 
make  a  good  road  material,  but  the  principle  must  be  kept 
always  in  mind  that  too  much  of  a  too  fine  material  will 
take  in  and  retain  so  much  water  that  the  binding  quality 
of  the  water  is  lost.  These  gravelly  clays  occur  in  many 
of  the  hills  of  the  glaciated  portions  of  the  United  States 
and  through  which  roads  are  often  cut. 

573.  Gravel  Roads. — In  the  construction  of  a  gravel  road, 
as  in  that  of  a  stone  road,  it  is  of  prime  importance  to  se- 
cure  first  of  all  a  properly  shaped  and  thoroughly  rolled 
and  firmed  road-bed  before  any  gravel  is  laid  on.  When 
this  has  been  done,  and  a  suitable  gravel  has  been  found, 
the  next  step  is  to  spread  evenly  over  the  surface  and  thor- 
oughly roll  a  layer  which,  when  finished,  will  measure  three 
inches  thick. 


460  Farm  Mechanics. 

In  the  rolling  it  will  be  important  to  firm  the  outer  edges 
of  the  gravel  first  in  order  that  the  rolling  may  not  force  it 
outward  and  destroy  the  slope.  Should  the  gravel  be  too 
dry  to  pack  it  must  be  moistened  or  the  work  be  suspended 
to  take  advantage  of  the  rains. 

To  make  a  good  road  there  should  be  not  less  than  three 
3-inch  layers,  and  usually  four  will  be  better.  Of  course 
a  road  6  inches  thick  will  be  a  great  improvement,  and 
often  where  the  travel  is  light  and  the  road-bed  thoroughly 
made,  three  inches  of  good  gravel,  well  placed,  will  make  a 
great  improvement  in  the  road,  serving  as  a  wearing  sur- 
face. 

Where  the  gravel  must  be  crushed  and  screened  to  secure 
the  proper  sizes  the  revolving  screen  represented  in  Fig. 
216  should  be  used  and  should  have  two  sizes  of  holes  1.5  to 
2  inch  and  3  to  4  inch  in  diameter.  The  coarser  size  of 
gravel  will  form  the  body  of  the  road  while  the  finer  will 
have  to  be  discarded  unless  it  happens  to  be  of  the  right 
quality  to  use  as  a  binding  material  or  in  making  a  bicycle 
path  along  one  side  of  the  road. 

574.  Roads  in  Swampy  Places. — It  occasionally  happens 
that  roads  must  be  built  in  places  which  cannot  be  drained 
and  which  are  too  soft  to  permit  of  the  construction  of  a 
solid  earth  foundation.  A  common  way  to  meet  this  type 
of  conditions  is  to  lay  a  foundation  of  logs,  poles  or  even 
brush,  having  the  desired  width  of  the  road  and  of  suffi- 
cient body  to  enable  an  earth  or  gravel  road  to  be  built  upon 
it.  When  such  roads  are  built  in  situations  where  the  wood 
is  kept  constantly  beneath  the  water  it  does  not  decay  and 
a  road  of  considerable  permanence  and  solidity  is  secured. 

Where  logs  are  used  care  is  taken  to  arrange  them  at 
right  angles  to  the  direction  of  the  road,  parallel  with  one 
another  and  like  sizes  side  by  side.  The  depressions  be- 
tween the  logs  are  filled  with  smaller  logs  or  poles,  whole 
or  split,  while  these  in  turn  may  be  covered  with  twigs  and 
limbs  forming  a  mat  upon  which  the  earth  or  gravel  road 
is  built.  Upon  this  mat  of  wood  is  usually  first  thrown 


Stone  Roads. 


461 


the  material  taken  from  ditches  on  either  side  made  for 
drainage,  building1  the  earth  or  gravel  road  upon  this  after 
it  has  first  been  well  spread  and  firmed. 


STONE   KOADS. 

Stone  roads  of  one  form  or  another  date  back  to  and  pos- 
sibly beyond  Roman  times;  and  Fig.  217  represents  two 
types  of  the  extremely  massive  and  substantial  roads 
which  were  built  ten  or  fifteen  centuries  ago,  some  of 
which  still  survive.  These  roads  had  a  width  of  30  feet 
and  pavements  of  heavy  stone  at  the  bottom  and  often  one 
or  more  layers  of  stone  bedded  in  cement  to  make  the  road 
water  proof.  One  type  of  construction  which  they  fol- 
lowed made  the  road  consist  of  four  layers : 


FIG.  217. —  Two  types  of  Ancient  Roman  stone  roads.     (After  Shaler.) 

1.  Two  or  three  courses  of  flat  stone  or,  if  these  were  not 
obtainable,  of  other  stone,  generally  laid  in  mortar. 

2.  A  layer  of  rubble  masonry  or  coarse  concrete. 

3.  A  finer  concrete  upon  which  was  laid 

4.  A  layer  of  paving  blocks  jointed  with  the  greatest 
nicety. 

It  is  stated  that  with  many  of  the  great  roads  the  paved 
portion  had  a  width  of  16  feet  bordered  by  raised  stone 


462  Farm  Mechanics. 

causeways  *outside  of  which,  on  each  side,  were  unpaved 
side-ways  each  eight  feet  wide,  and  the  paved  way  some- 
times had  an  aggregate  thickness  of  three  feet. 

575.  Macadam  Roads. — The  use  of  crushed  rock  in  road 
building  is  at  least  as  old  as  Roman  history  ;  but  as,  during 
the  dark  ages,  little  road  building  of  a  permanent  character 
was  practiced,  the  art  had  to  be  revived  in  modern  times 
and  about  1764  the  French  engineer  Tresaguet  appears  to 
have  introduced  into  France  the  type  of  road  represented  in 
Fig.  218,  consisting  of  a  stone  pavement  covered  with  two 
or  three  inches  of  crushed  rock  as  a  facing  material.  After 
being  introduced  into  England  and  Scotland,  where  the  de- 
tails were  modified  and  perfected  by  Telford  about  1820, 
this  type  of  stone  construction  came  to  be  known  as  the 
Telford  road. 


FIG.  218.— Type  of  road  introduced  into  France  by  Tresaguet  about  1764. 
(After  Shaler.) 

Macadam's  work  began  somewhat  earlier  than  Telford's 
in  1816,  and  to  him  apparently  is  due  the  idea  that  when 
any  road-bed  is  thoroughly  under- drained,  so  as  to  remain 
permanently  hard,  then  crushed  stone  alone  may  be  used, 
the  pavement  of  Roman  practice  becoming  unnecessary. 

576.  Construction  of  Macadam  Roads. — After  the  founda- 
tion for  the  stone  road  has  been  completed  the  border  is 
left  with  a  shoulder  of  earth  on  each  side  as  represented  in 
Fig.  219,  between  which  the  road-bed  is  covered  with  a 
layer  of  crushed  rock  as  nearly  one  size  as  possible  and 
three  or  four  inches  thick.  This  layer  is  next  thoroughly 
rolled  and  then  covered  with  enough  of  finely  crushed  rock 
to  fill  the  voids  between  the  larger  fragments.  This  ma- 
terial is  worked  in  with  the  roller  and  water  until  a  solid 
bed  has  been  formed. 


Stone  Roads.  463 

After  the  first  layer  has  been  placed  the  second  is  ap- 
plied in  the  same  manner,  rolled,  and  the  binding  material 
applied  and  again  rolled,  until  thorough  consolidation  has 
been  secured. 


FIG.  219. — View  showing  the  road-bed,  in  the  foreground,  shaped  with  road 
grader  and  receiving  the  foundation  layer  of  crushed  rock  4  inches  thick. 

577.  .Fitting  the  Road-bed. — It  is  of  the  utmost  impor- 
tance to  have  a  thoroughly  firmed  and  seasoned  road-bed 
put  into  proper  form  and  well  drained  before  the  stone  sur- 
face is  to  be  applied,  and  to  do  this  most  economically  it  is 
well  to  do  all  of  this  preliminary  work  a  year  or  more  ahead 
so  that  traffic,  rains  and  frosts  shall  have  an  opportunity  to 
do  the  work  of  consolidation,  and  to  discover  the  soft  places 
which  may  exist.  In  short,  the  formation  of  a  good  earth 
road  to  be  used  for  a  number  of  years  as  such  will  generally 
be  found  the  best  and  most  economical  preparation  for  the 
stone  road. 

578.  Forming  the  Shoulders. — The  formation  of  the  shoul- 
ders represented  in  the  foreground  of  Fig.  219  is  best  done 


464  Farm  Mechanics. 

with  a  road  grader  or  road  machine.  With  this  tool  the 
surface  of  the  road-bed  is  prepared  at  the  same  time  and  the 
shoulders  left  in  such  shape  that  very  little  hand  labor  will 
be  required  for  the  finishing  touches.  After  the  shoulders 
have  been  roughly  formed  and  before  the  finishing  touches 
are  given  the  roller  should  go  over  the  road-bed  to  make 
sure  that  it  is  properly  firmed  and  that  there  are  no  soft 
places. 

579.  Kinds  of  Rock  for  the  Road. — Practical  experience 
has  demonstrated  that  the  best  rocks  for  road  making  are 
the  dark  green,  black  and  dark  gray  trap  or  igneous  rock 
such  as  are  known  in  common  language  as  "nigger  heads" 
in  glaciated  countries  where  large  boulders  are  common  in 
the  fields  and  cuts  of  roads.  They  are  tough,  fine  grained 
rock,  much  less  brittle  than  most  others,  which  yield  when 
grinding  upon  themselves  and  under  the  wheel  a  fine  rock 
flour  whose  texture  is  such  that  it  holds  the  needed  amount 
of  moisture  to  make  it  bind  together  well,  and  consequently 
a  road  built  from  these  fragments  sets  sooner  than  almost 
any  other  crystalline  rock  and  hence  is  subject  to  less  in- 
ternal wear. 

Next  to  the  trap  rock  in  value  for  road  building  purposes 
stand  the  closer  grained  hornblend-bearing  syenites  and 
gneisses  which  are  species  of  granite  where  hornblend  takes 
the  place  of  mica  of  the  true  granites.  It  is  the  class  of 
dark  minerals  allied  to  hornblend  composing  much  of  the 
trap  rock  referred  to  above  which  makes  that  the  best  road 
stone. 

Next  in  order  stand  the  true  granites  made  up  of  quartz, 
feldspar  and  mica,  and  their  gncissoid  varieties.  The  best 
of  this  class  of  rocks  are  the  close  fine-grained  varieties 
having  the  least  tendency  to  break  into  thin  layers,  giving 
flat  instead  of  cubical  blocks. 

To  the  granites  and  syenites  with  their  banded  or  gneiss- 
oid  varieties  belong  the  lighter  colored  and  flesh  colored 
boulders  which  are  usually  associated  with  the  "nigger 
heads"  of  glacial  drift. 


Stone  Roads. 


465 


The  chief  difficulty  with  syenites  and  granites  for  road 
metal  is  their  brittle,  unyielding  quality  and  coarse  crystal- 
line structure  which  makes  them  grind  and  pound  up  into 
a  coarse  sand  without  a  sufficient  amount  of  the  finest  dust 
to  give  it  the  needed  water-holding  power  to  permit  it  to 
properly  bind  the  pieces  together.  The  road-bed  fails  to 


FIG.  220.  — View  showing  where  four  inches  of  crashed  rock  for  wearing  surface 
is  being  built  upon  four  inches  of  road-gravel  as  foundation  layer. 

set  quickly  and  the  internal  wear  is  larger  while  there  is  a 
greater  tendency  for  ruts  to  form  in  wet  weather  and  for 
the  surface  to  ravel  or  throw  out  loose  pieces  in  a  dry  time. 
Next  to  the  syenites  and  granites  in  general  availability 
for  road  metal  stand  the  close  grained  hard  limestones 


466  Farm  Mechanics. 

which  break  into  hard,  clean  blocks  and  fragments  with 
sharp  edges  and  little  material  which  will  rub  off  under  the 
fingers.  Any  rock  which  crushes  readily  into  an  earth- 
like  or  sandy  material  will  not  answer  for  road  work. 

When  a  good  road  limestone  wears  down  under  the 
wheels,  the  horses'  feet  or  the  roller,  a  loam-like  powder  is 
formed  which  holds  the  right  amount  of  water  for  good 
binding,  and  besides  this  it  appears  more  quickly  to  pass 
into  that  cementing  stage  which  in  nature  cements  beds  of 
loose  fragments  into  rock. 

The  chief  objection  to  limestone  as  a  road  metal  is  its 
softness,  which  permits  it  to  wear  away  rapidly,  leaving 
the  surface  dusty  in  dry  and  muddy  in  wet  weather. 

The  extremely  hard  and  brittle  quartzite  which  throws 
off  angular  bits  under  the  blows  of  horses'  feet  and  the  roll- 
ing of  wheels  makes  one  of  the  poorest  road  materials  be- 
cause it  too  nearly  possesses  glass-like  brittleness  and  the 
dust  is  too  coarse  and  sand-like  to  hold  the  needed  water  for 
binding. 

580.  Foundation  and  Surfacing  Stone  May  be  Different — 
Where  there  is  in  the  locality  a  rock  which  does  not  make  a 
good  wearing  surface  but  which  binds  well,  like  limestone, 
this  may  be  used  to  advantage  for  the  foundation  of  coun- 
try roads,  thus  making  it  necessary  to  import  only  the  wear- 
ing surface  layer. 

581.  Sorting   Boulders   Before    Crushing. — In    localities 
where  there  are  many  boulders  available  for  road  work 
it  will  often  be  practicable  to  sort  these  when  hauling  them 
to  the  crusher  in  such  manner  as  to  use  the  lighter  colored 
varieties  for  the  foundation,   reserving  all  of  the  "nigger 
heads"  for  the  surface  layer,  and  in  this  way  increase  the 
efficiency  of  the  material. 

582.  TJsing  Limestone  for  Binding. — Where  only  granitic 
rock  and  quartzite  are  available  for  road  work  and  these  do 
not  bind  well,  it  will  often  happen  that  the  limestone  of 


Stone  Roads.  467 

the  locality  may  be  crushed  fine  to  form  screenings  and 
used  to  great  advantage  as  a  binding  material  to  hold  the 
harder  rocks  more  securely  in  place.  This  practice  would 
be  especially  desirable  for  the  foundation  layer  where  it 
could  not  be  converted  into  dust.  But  in  localities  where 
both  limestone  and  the  harder  rock  are  available,  but  where 
the  limestone  can  be  obtained  at  much  the  less  cost,  this 
may  be  used  alone  for  the  foundation  and  as  a  binding  ma- 
terial for  the  surface  layer. 

583.  Roads  Made  Without  Binding  Material. — It  was  Ma- 
cadam's practice  in  road  building  to  strictly  forbid  the  use 
of  all  binding  material  whatsoever.     He  preferred  to  wait 
for  the  general  traffic  over  the  road  to  develop  from  tho 
wear  of  the  crushed  stone,  both  superficial  and  internal, 
the  necessary  amount  of  rock  flour  to  do  the  work  of  filling 
and  cementing.     While  this  work  was  in  progress  the  road 
was  given  constant  supervision  to  keep  it  in  proper  form. 
At  the  same  time  the  filling  and  binding  material  was  be- 
ing slowly  produced  there  was  brought  upon  the  road  with 
the  wheels  and  horses'  feet  a  considerable  amount  of  earth 
which  slowly  worked  downward  and  united  with  the  rock 
flour  to  complete  the  consolidation.      Macadam  certainly 
secured  in  the  end  a  better  road  by  this  method  than  was 
usually  secured  with  the  use  of  the  then  available  binding 
material. 

It  must  be  remembered,  however,  that  in  his  time  rock 
were  crushed  by  hand  and  little  fine  material  was  made  to 
use  for  binding,  whereas  with  the  modern  rock  crushers  a 
large  amount  of  this  material  is  produced  which  must  be  a 
dead  loss  if  it  cannot  be  used  for  binding  and  surfacing, 
and  it  is  quite  certain  that  had  Macadam  used  our  modern 
rock  crushers  he  would  have  availed  himself  of  the  screen- 
ings. 

584.  Use  of  Sand  for  Binding. — The  great  readiness  with 
which  clean  dry  sand  works  into  and  fills  the  voids  between 
the  stone  of  a  road,  the  ease  with  which  it  may  be  handled 


468 


Farm  Mechanics. 


and  the  readiness  with  which  it  may  often  be  obtained, 
leads  to  its  occasional  use  as  a  binding  material  in  macadam 
road.  The  coarse  silicious  sands,  however,  have  very  little 
cementing  quality,  they  do  not  retain  water  well  enough 
cither  to  make  the  road  shed  the  rains  nor  give  the  surface 
tension  of  water  much  opportunity  to  bind  the  grains  to- 


FIG.  221.  — View  showing  the  binding  material  or  screenings  being  applied  to  the 
foundation  layer  of  crushed  rock. 


gether  firmly;  consequently  the  best  results  cannot  be  se- 
cured when  it  is  used. 

If  loam  is  used  there  is  danger  that  it  will  pack  in  the 
upper  surface  of  the  layer  of  stone  and  prevent  even  the 
combined  use  of  water  and  the  roller  from  working  it  to 


Stone  Roads. 


469 


the  bottom  so  as  to  completely  fill  the  voids.  There  is  the 
still  further  danger  that  it  will  work  in  between  the  tlat 
surfaces  of  the  crushed  rock,  holding  them  apart  to  such  an 
extent  that  heavy  loads  will  produce  too  much  rocking  of 
the  pieces  and  quickly  lead  to  the  formation  of  ruts.  It 
the  loam  could  be  had  in  a  dry  condition,  such  as  is  usually 
the  case  with  the  screenings  and  the  sand,  it  would  be  possi- 
ble with  dry  rolling  to  nearly  completely  fill  the  voids  so 
that  the  subsequent  use  of  water  would,  with  the  roller,  lead 
to  good  results. 

585.  Limestone  for  Stone  Roads. — There  is  no  doubt  that 
crushed  limestone  although  a  soft  rock  will  make  an  excel- 


FIG.  222.— View  of  distributing  cart  being  raised  to  spread  crushed  rock. 


lent  country  road  where  the  traffic  is  not  heavy  and  the 
use  of  it  should  be  encouraged  wherever  suitable  quality  of 
rock  is  available.     There  is  no  rock  which  breaks  in  better 
30 


470 


Farm  Mechanics. 


form  or  which  binds  as  well  and  sets  as  quickly.  It  is 
readily  quarried  and  put  in  shape  for  the  crusher ;  and  the 
power  required  for  crushing  being  small  makes  it  less  bur- 
densome for  towns  to  invest  in  the  necessary  machinery. 

It  is  true  that  the  road  wears  rapidly  under  heavy  traffic 
and  the  surface  becomes  dusty  in  a  dry  time,  but  not  more 
so  than  clay  roads  do.  It  is  true  that  careful  road  engi- 
neers advise  against  its  use,  but  it  is  usually  from  the  stand- 
point of  city  and  suburban  traffic  rather  than  from  that  of 
the  purely  country  road. 


FIG.  223.— View  of  distributing  cart  spreading  crushed  rock  on  the  road. 

586.  Spreading  the  Rock  on  the  Road-bed. — It  is  import- 
ant that  the  crushed  rock  should  be  laid  down  on  the  road- 
bed in  a  sheet  both  of  uniform  thickness  and  uniform  den- 
sity and  where  this  is  not  done  the  road  is  quite  certain  to 
roll  to  an  uneven  surface  which  will  make  it  necessary  to 
add  more  material  in  some  places  and  remove  it  in  others. 
But  this  will  unnecessarily  add  to  the  cost  of  the  road. 


Stone  Roads. 


471 


Not  only  this,  but  when  a  wagon-load  of  stone  is  all  dumped 
in  one  place,  leaving  it  for  a  man  to  spread,  it  is  certain 
to  occur  that  all  of  the  dust  and  fine  materials  not  removed 
by  the  screen  will  drop  into  the  voids  at  the  place  where 


FIG.  224. —  View  of  surfacing  crushed  rock  as  left  by  the  distributing  cart  on  the 
road.  The  watch,  2  inches  in  diameter,  serves  as  a  scale  to  show  the  size  of 
the  rock  fragments. 

the  load  was  left  and  this  will  give  rise  to  a  spot  more  com- 
pacted than  the  balance  of  the  road  and  hence  when  it  cornea 
into  service  two  ruts  or  depressions  are  liable  to  form  one 
on  either  side  of  the  harder  spot. 


472 


Farm  Mechanics. 


To  avoid  these  difficulties  and  to  save  time  in  spreading 
the  material  the  distributing  cart  represented  in  Figs.  222 
and  223  has  been  devised.  In  it  can  be  placed  two  cubic 
yards  of  rock,  and  after  tilting  the  box  as  shown  in  Fig.  222 
the  end  board  may  be  opened  to  such  a  width  as  to  deposit 


FIG.  225.—  View  of  the  surfacing  rock  after  it  has  been  packed  by  the  roller. 


a  uniform  layer  of  any  desired  thickness  while  the  team 
travels  along  at  a  slow  and  uniform  pace.  Fig.  224  is  a 
view  showing  how  the  surface  was  left  by  the  distributing 


Stone  Roads.  473 

cart  and  the  watch  is  a  scale  by  which  the  size  of  the  pieces 
may  be  judged,  its  diameter  being  a  trifle  less  than  two 
inches. 

587.  Thickness   of   Layer. — The   thickness    of   a   layer 
placed  at  one  time  should  vary  somewhat  with  the  size  of 
the  pieces,  the  depth  being  greater  with  the  larger  frag- 
ments.   With  pieces  of  the  size  shown  in  Fig.  224  the  layer 
when  packed  should  not  be  greater  than  four  inches  and 
three  inches  will  pack  more  quickly  and  closely  than  four 
inches.     A  too  thick  layer  tends  to  form  a  crust  on  the  sur- 
face,   making  it  difficult   to  fill  all  the  voids  below  com- 
pletely. 

588.  Rolling. — The  function  of  rolling  is  to  arrange  the 
fragments  in  the  positions  of  the  greatest  stability  with  ref- 
erence to  the  rolling  of  wheels  and  the  tramping  of  horses. 
The  first  effect  of  the  roller  is  to  bring  the  pieces  nearer 
together  and  to  reduce  the  size  of  the  voids.     This  is  clearly 
brought  out  by  the  two  photo-engravings,  Figs.  224  and 
225. 

There  is  one  other  important  thing  which  rolling  should 
secure  and  that  is  to  put  the  several  pieces  of  stone  together 
in  the  positions  of  the  most  stable  equilibrium ;  that  is,  in 
positions  such  as  to  make  certain  that  they  shall  not  tip 
or  turn  when  the  stress  of  the  wagon  or  team  is  brought 
upon  them. 

589.  Size  and  Weight  of  Roller. — The  diameter  of  the 
roller  should  be  large  to  prevent  it  from  shoving  the  stone 
forward  as  it  moves  and  in  order  that  the  thrust  may  be  as 
nearly  directly  downward  as  possible.     It  will  be  observed 
that  even  the  front  wheel  of  a  loaded  wagon  often  slides 
rather  than  rolls  when  coming  upon  the  unpacked  layer  of 
rock  on  the  road,  and  such  movement  cannot  do  proper 
packing. 

There  appears  to  be  a  lack  of  agreement  between  prac- 
tical men  regarding  the  proper  weight  of  the  roller,  some 


474 


Farm  Mechanics. 


advocating  a  roller  of  3.5  to  5.5  tons,  while  others  hold 
that  only  one  of  15  to  20  tons  weight  will  serve  the  purpose. 
Others  advocate  a  light  weight  to  begin  with  and  a  heavier 
one  at  the  close. 


FIG.  226.— View  showing  horse  roller  at  work  compacting  the  road  metal. 


590.  Amount  of  Rolling. — The  only  general  rule  which 
can  be  given  in  regard  to  the  amount  of  rolling  a  given 
layer  should  receive  is  that  the  work  should  be  continued 
until  the  stones  cease  to  move  in  front  of  the  roller  or  un- 
til the  roller  no  longer  sensibly  depresses  the  bed  and  it 
has  become  hard  and  smooth.  It  should  be  kept  in  mind, 
however,  that  the  road  may  be  rolled  too  much,  or  until 


Stone  Roads.  475 

the  stone  again  begin  to  move.     This  is  most  likely  to  oc- 
cur when  the  stone  is  too  dry. 

591.  Manner  of  Rolling. — The  rolling  should  begin  at  the 
outer  sides  of  the  road,  packing  the  stone  first  against  the 
shoulder.     If  this  is  not  done  the  fact  that  the  road-bed 
is  highest  in  the  center  will  lead  to  flattening  the  slope  and 
thinning  out  the  rock  in  the  center  through  a  side  creeping 
of  the  material  from  under  the  roller. 

592.  Kind  of  Roller. — There  are  three  methods  of  consol- 
idating the  layers  of  stone  put  into  a  road.     The  first,  now 
largely  abandoned  as  being  too  expensive  and  too  uncertain, 
is  to  allow  it  to  be  done  by  the  natural  traffic.     The  second, 
also  being  abandoned  as  too  expensive,  is  the  use  of  a  3.5 
to  5-ton  horse  roller ;  and  the  third,  which  is  regarded  the 
cheapest  and  best,  is  with  the  aid  of  an  8  to  20-ton  steam 
roller. 

The  safest  indications  seem  to  point  to  the  use  on  coun- 
try roads  of  an  8  to  10-ton  steam  roller  as  most  satisfactory ; 
although  good  work  can  be  done  with  the  horse  roller  of 
half  this  weight  which  may  be  made  heavier  or  lighter  by 
taking  on  and  laying  off  weights  Such  a  roller  as  this  is 
represented  in  Fig.  226  which,  naked,  weighs  3.5  tons, 
but  by  the  addition  of  castings  to  the  inside  of  the  roller 
may  be  increased  to  5.5  tons.  This  roller  has  the  frame 
and  tongue  so  constructed  that  the  team  may  be  turned 
without  reversing  the  roller,  a  very  important  feature. 

It  will  be  readily  seen  that  the  use  of  two  men  and  two 
teams  must  make  the  service  of  this  roller  very  expensive, 
and  when  the  disturbing  effects  of  the  horses'  feet  are  re- 
called it  becomes  clear  that  the  steam  roller  easily  managed 
by  one  man  is  much  better. 

593.  Rock  Crushers. — Until  recently  all  rock  crushing  for 
road  work  has  been  done  by  hand  and  hammer,  and  in  the 
days  of  slave  labor  when  the  man  was  a  machine  which 
managed,  fed,  cared  for  and  reproduced  itself,  it  is  clear 


476 


Farm  Mechanics. 


how  such  Herculean  tasks  as  the  ancient  Roman  roads  could 
be  accomplished.  But  happily,  the  use  of  steel  and  iriani- 
mate  forces  is  freeing  man  from  such  drudgery ;  and  in 
Figs.  227  and  228  are  two  views  of  a  rock  crusher  at  work, 
breaking  stone,  sorting  it  and  delivering  it  into  bins 
where  it  may  easily  be  dropped  into  wagons  for  delivery 
upon  the  road. 


FIG.  227. — View  of  No.  3  Austin  Crusher,  with  revolving  soreon  bronklng 
boulders  for  road;  and  wagon  loading  coarsest  grade  of  broken  stone. 

At  the  time  these  views  were  taken  the  crusher  was  be- 
ing driven  by  a  22  H.  P.  traction  engine  and  was  crushing 
rock  at  the  rate  of  100  wagon  loads  per  day.  The  material 
is  separated  into  three  sizes,  the  coarsest  used  for  the  foun- 
dation, the  intermediate  for  the  wearing  surface  and  the 
finest  as  binding  and  surfacing  material,  and  Fig.  227 
shows  a  wagon  loading  with  the  foundation  size,  and  Fig. 
228  with  the  screenings  or  binding  material. 

There  are  various  forms  of  crushers  on  the  market  and 
Fig.  216  represents  another  type. 


Stone  Roads. 


477 


594.  Revolving  Screen. — The  revolving  screen  is  an  indis- 
pensable attachment  to  a  rock  crusher,  because  a  good  road 
cannot  be  made  with  the  unsorted  material,  for  with  this 
method  of  putting  the  crushed  rock  upon  the  road  the  fine 
materials  are  certain  to  work  downward  and  the  coarser 
fragments  to  come  to  the  surface.  It  should  be  thoroughly 
understood  too  that  the  chute  screen  will  not  do  the  work. 


FIG.  228. — Side  view  of  No.  3  Austin  Crusher  and  wagon  loading  screenings. 


595.  Earth  and  Stone  Road  Combined. — Where  it  is  de- 
sired to  cheapen  the  construction  of  stone  roads  it  is  prac- 
ticable to  make  the  central  portion  8  feet  wide  of  this  ma- 
terial and  then  have  on  one  or  both  sides  an  earth  road 
of  eight  feet,  giving  a  total  width  of  16  or  24  feet  to  the 
margin  of  grass  and  30  feet  to  the  side  ditches.  The  most 
serious  objection  to  this  combined  plan  is  the  securing  at 
all  times  of  sufficient  and  quick  surface  drainage. 

The  chief  difficulty  which  will  arise  in  the  carrying  out 


478 


Farm  Mechanics. 


of  this  plan  will  come  from  the  tendency  of  summer  traffic 
on  the  narrow  earth  road  to  go  so  persistently  in  one  track 
as  to  develop  wheel  and  foot  ways  deep  enough  to  prevent 
surface  drainage.  The  fact  that  the  stone  road  may  come 
into  service  when  the  ground  is  wet  will  only  lessen  the 
tendency  to  develop  the  evil  pointed  out  but  riot  prevent 
it.  For  winter  service  in  cold  climates  it  seems  clear  that 
the  earth  road  will  be  likely  to  ensure  better  sleighing. 


0TT. 


FIQ.  229.— Diagrams  showing  profiles  of  earth  and  stone  road  combined. 

596.  Telford  Foundation — When  it  is  necessary  to  build 
the  road  where  the  ground  is  soft  then  it  may  be  best  to 
lay  a  foundation  of  larger  stone  as  was  the  general  practice 
with  the  Komans  and  with  the  English  engineer,  Telford, 
whose  name  is  now  attached  to  this  type  of  road  founda- 
tion. The  paving  blocks  should  be  uniform  in  size,  laid 
in  rows  across  the  road  after  it  has  been  given  the  proper 
slope,  the  pieces  breaking  joints.  The  stones  should  not 


Stone  Roads. 


479 


exceed  10  inches  in  length,  6  inches  wide  on  the  bottom 
and  4  inches  at  the  top,  the  thickness  being  4  or  5  inches 
for  a  road  8  inches  thick.  The  surface  of  the  pavement 
foundation  should  be  as  even  as  practicable  and  the  voids 
filled  with  broken  stone.  It  is  necessary  to  have  each  piece 
thoroughly  bedded  before  the  macadam  material  is  added 
so  as  not  to  be  tilted  on  the  surface. 


PIG.  230. — View  showing  road  with  the  stone  portion  in  the  foreground  nearly 

completed. 

597.  Culverts. — Culverts  are  necessary  for  carrying  un- 
der a  road  the  water  from  adjacent  fields  which  collects  as 
surface  drainage  in  times  of  heavy  rains  and  melting  snows. 
The  permanent  forms  are  made  of  sewer  tile,  cement  tile, 


480  Farm  Mechanics. 

cast  iron  sewer  pipe  or  of  stone.  Wood  should  only  be 
used  as  a  temporary  expedient. 

Where  the  amount  of  water  to  be  conveyed  is  small  so 
as  to  demand  only  one,  two  or  three  12-inch  sewer,  or  ce- 
ment tile,  it  will  usually  be  cheapest  to  use  these,  but  where 
a  water-way  demanding  a  cross-section  of  more  than  8 
square  feet  is  necessary  and  where  stone  are  available,  it 
will  be  cheapest  to  make  it  of  arched  masonry. 

Where  the  culverts  are  of  sewer  pipe  there  should  be 
not  less  than  18  inches  of  earth  in  the  road  above  them  to 
prevent  crushing. 

The  cast  iron  pipe  is  the  safest  to  use  and  cheaper  than 
either  sewer  or  cement  tile  when  diameters  above  16  inches 
are  required. 


MAINTENANCE   OF  COUNTEY  EOADS. 

Important  as  the  matter  of  construction  of  good  roads 
is,  it  is,  or  should  be,  secondary  to  that  of  maintenance; 
when  a  good  thing  has  been  made  which  is  designed  for 
permanent  service  it  is  clearly  a  matter  of  sound  business 
policy  to  provide  whatever  economic  means  is  practicable 
for  keeping  it  in  order. 

598.  Section  Men  Necessary. — In  the  maintenance  of 
railroads  it  was  early  learned  that  two  or  more  men  pro- 
vided with  proper  tools  must  be  employed  by  the  year,  per- 
manently or  as  long  as  they  rendered  efficient  service,  to 
care  for  and  keep  in  order  a  certain  number  of  miles  of 
road.  It  is  the  business  of  these  men  to  daily  go  over  their 
section  and  keep  it  in  first  class  repair  and  their  tenure 
of  office  is  only  conditional  upon  their  doing  this  satisfac- 
torily. 

It  is  self-evident  that  good  country  roads  can  only  be 
maintained  by  adopting  and  keeping  in  force  a  system 
which  is  equivalent  to  that  found  indispensable  in  railroad 
maintenance.  That  is,  men  competent  to  do  the  work, 


Maintenance  of  Country  Roads. 


481 


provided  with  the  necessary  authority,  tools  and  materials, 
must  have  constant  employment  at  a  price  which  will  per- 
mit them  to  devote  their  time  to  it,  and  they  must  be  made 
responsible  for  the  maintenance  of  a  certain  number  of 
miles  of  road  365  days  in  a  year. 


FIG.  231. — View  of  country  stone  road  with  foot  path  on  one  side,  near  Maybole, 
Ayrshire,  Scotland.     From  photo  in  1£95. 

599.  Road  Master. — In  the  country  road  service  it  will 
be  necessary  to  have  one  man  who  corresponds  in  duties 
and  responsibilities  to  the  "Section  Boss"  of  the  railroad. 
He  must  be  competent,  temperate  and  in  every  way  relia- 
ble and  trustworthy.       He  must  have  a  practical  knowl- 
edge of  the  principles  and  details  underlying  the  main- 
tenance of  good  roads  and  at  his  command  the  necessary 
authority,  assistance  and  appliances  for  doing  the  work  re- 
quired. 

600.  Width  of  Tires  Controlled — When  we  come  to  have 
a  system  of  good  roads  and  the  means  for  maintaining  them 


482  Farm  Mechanics. 

it  will  be  necessary  to  have  ordinances  regulating  the  width 
of  tire  and  diameter  of  wheel  which  may  be  used  on  the 
roads  when  carrying  specified  loads.  In  Europe,  where 
better  roads  are  found  and  a  better  system  for  maintenance 
exists,  there  are  ordinances  which  fix  the  width  of  tire  to 
be  used  with  given  loads.  In  Bavaria  the  regulations  are 
as  follows : 

Two  wheel  carts  with  two  horses,  4.133  inch  tires. 

Two  wheel  carts  with  four  horses,  6.180  inch  tires. 

Four  wheel  carts  with  two  horses,  2.596  inch  tires. 

Four  wheel  carts  with  four  horses,  4.133  inch  tires. 

Four  wheel  carts  with  five  to  eight  horses,  6.180  inch 
tires. 

Carts  with  more  than  four  and  wagons  with  more  than 
eight  horses  are  not  allowed  to  use  the  roads  without  a 
special  permit  from  the  authorities. 

Other  countries  of  the  Old  World  have  found  similar 
ordinances  necessary  and  it  is  clearly  rational  and  just 
that  such  matters  should  be  regulated,  for  otherwise  one 
man  may  easily  put  in  jeopardy  the  interests  of  a  whole 
community. 

601.  Maintenance    and    Repairs. — A    sharp    distinction 
should  always  be  made  between  the  maintenance  of  a  road 
and  its  repairs.       It  is  only  when  some  accident  has  oc- 
curred to  seriously  injure  a  road    or    when,    from    long 
neglect,  it  has  become  well  nigh  worn  out  that  repairs  are 
needed,    but   the    daily  touching  up  of  slight  defects  and 
places  of  evident  wear  constitutes  maintenance. 

602.  Good  Maintenance. — Good  maintenance  will  con- 
sist in  daily  attention  to  all  the  details  which  are  necessary 
to  keep  a  section  of  road  up  to  the  standard  of  perfection 
practicable  to  its  type,  influenced  by  its  local  surroundings 
and  conditions.     It  must  consist  in  (1)  keeping  the  road 
in  proper  form;  (2)  in  adding  materials  to  the  wearing 
surface  where  needed;    (3)  in  keeping    the  road  surface 
and  drainage  channels  clean ;  (4)  in  keeping  the  road  sides 


Maintenance  of  Country  Roads. 


483 


free  from  weeds  and  otherwise  neat;  (5)  in  caring  for  and 
maintaining  road  trees  if  they  are  grown;  (G)  in  main- 
taining the  proper  conditions  in  winter  in  regard  to  snow. 

603.  Maintenance  of  Earth  and  Gravel  Roads. — The  first 
requisite  for  the  maintenance  of  any  road  is  the  knowledge 
which  can  be  gained  by  going  over  the  road  while  or  im- 
mediately after  it  rains.  Observations  at  this  time 
will  show  the  road  master  where  the  most  serious  defects 
exist  and  he  should  make  careful  note  of  them  to  use  in 
directing  his  efforts  as  soon  as  the  weather  permits.  It 
should  therefore  be  the  business  of  the  road  master  to  study 
his  roads  in  wet  weather  and  he  should  be  equipped  with 
clothing,  etc.,  in  a  way  which  will  permit  him  to  do  this 
without  risk  of  injury  to  health. 


FIG.   232.— View   of   French   country  road   20   feet   wide,    showing   piles  of 
crushed  limestone  used  in  maintenance.    1'uoto.  in  1895,  near  Grfgnon. 

Whenever  ruts  or  saucers  begin  to  show  in  the  road  they 
should  be  corrected  immediately,  provided  the  moisture 


484 


Farm  Mechanics. 


conditions  permit  of  doing  so,  but  on  the  earth  roads  the 
soil  may  be  either  too  Avct  or  too  dry  to  allow  this  to  be 
done  well,  and  the  highest  success  will  be  attained  when  the 
road  master  comes  to  know  and  understand  his  conditions 
and  then  is  alert  to  move  at  just  the  right  time.  The  ruts 
will  be  formed  chiefly  in  both  the  very  wet  and  the  very  dry 
weather,  and  in  the  country  where  sprinkling  the  roads 
cannot  be  afforded,  everything  must  be  planned  to  take  ad- 
vantage of  every  shower  heavy  enough  to  bring  the  road 
into  condition  for  working  with  grader,  shovel,  rake  and 
roller. 


FIG.  233. —  View  on  the  same  road  showing  the  tool  house  where  appliances  for 
caring  for  the  road  are  kept.    Photo,  in  1895,  near  Griguon. 

The  intelligent  use  of  the  grader  and  roller  at  the  right 
time  after  the  rains  of  a  wet  period  and  after  a  dry  period 
will  make  marvelous  changes  in  the  character  of  earth  roads 
of  all  classes  and  particularly  in  those  which  are  proverb- 
ially bad. 


Maintenance  of  Country  Roads.  485 

We  cannot  too  strongly  emphasize  that  to  drive  up  one 
side  of  the  road  with  a  road  machine  and  back  on  the  other, 
scraping  a  lot  of  loose,  heterogeneous  rubbish  and  earth 
into  the  middle  of  the  road,  to  be  tramped  out  again  by 
the  traffic,  is  neither  repairing  nor  maintaining  the  road. 
The  material  brought  upon  the  road  should  be  well  dis- 
tributed and  harrowed  until  an  even,  uniform  layer  has 
been  secured  and  then  the  roller  should  be  thoroughly  ap- 
plied when  the  earth  is  in  just  the  right  condition  to  pack 
well.  Work  of  this  sort  will  count  and  will  be  appreciated. 

31 


CHAPTER  XXII. 
FARM   MOTORS. 

The  tendency  of  modern  civilization  is  toward  the  adop- 
tion of  methods  and  appliances  which  free  man  from  the 
necessity  of  expending  his  strength  in  developing  mere 
mechanical  power  such  as  a  horse,  a  windmill  or  an  engine 
may  create,  and  thus  to  leave  him  greater  freedom  to  devote 
a  larger  share  of  his  time  and  energies  to  lines  of  mental 
activity,  the  necessity  for  which  becomes  greater  and 
greater  as  competition  becomes  wider  and  more  intense. 
As  a  result  of  this  tendency  farm  machines  are  steadily  in- 
creasing, becoming  more  complicated  and  demanding  more 
and  more  the  employment  of  one  or  another  form  of  motor 
or  engine  to  drive  them.  This  in  turn  makes  it  necessary 
for  the  farmer  to  know  more  of  mechanical  principles,  and 
how  to  handle  and  care  for  machinery  than  was  formerly 
necessary. 

604.  Farm  Motors. — The  sources  of  energy  which  are 
used  on  the  farm  to  drive  machinery  are  (1)  animal 
motors,  (2)  wind  motors,  (3)  water  motors,  (4)  steam 
motors,  (5)  oil  motors  and  (6)  electric  motors. 

All  of  these  motors  are  machines  designed  to  utilize  the 
energy  of  (1)  chemical  action,  (2)  moving  air  and  (3) 
running  water.  The  horse,  the  steam  engine  and  the  oil 
engine  each  derives  its  power  from  the  chemical  action  of 
the  fuel  consumed  or  food  eaten  and  may  therefore  be 
called  chemical  engines ;  the  windmill  and  the  water  wheel 
get  their  power  by  arresting  the  motion  of  wind  or  water, 
actuated  by  the  force  of  gravity,  and  these  may  be  called 
gravitation  engines.  The  chemical  engines  use  the  energy 


(Animals  as  Motors.  487 

derived  from  the  collision  of  molecules  and  atoms,  while 
the  gravitation  engines  use  the  energy  derived  from  the 
movement  of  streams  of  air  or  water  traveling  as  a  body. 

ANIMALS  AS   MOTOES. 

When  animals  are  viewed  from  the  standpoint  of  ma- 
chines they  are  wonderful  mechanisms.  Xot  only  are  they 
self-feeding,  self-controlling,  self-maintaining  and  self-re- 
producing, but  they  are  far  more  economical  in  the  energy 
they  are  able  to  develop  from  a  given  weight  of  fuel  ma- 
terial, than  any  other  existing  form  of  motor. 

While  they  are  like  the  steam  engine  in  requiring  car- 
bonaceous fuel,  oxygen  and  water  for  use  in  developing 
energy  these  are  made  to  combine  in  the  animal  body  at  a 
much  lower  temperature  than  is  possible  in  the  steam  en- 
gine, and  a  much  smaller  proportion  of  the  fuel  value  is 
lost  in  the  form  of  heat,  when  work  is  being  done. 

605.  The   Horse   as   a   Motor. — The   essential   elements 
which  constitute  the  horse  a  machine  for  developing  power 
are  (1)  a  system  of  rigid  levers  united  by  ligaments  and 
capsules  at  the  joints  which  are  automatically  lubricated 
by  a  synovial  fluid;  (2)  a  system  of  muscles,  each  one  of 
which  is  a  motor,  corresponding  in  function  to  the  piston 
and  cylinder  of  a  steam  engine;  (3)  a  fuel  supplying  and 
waste  removing  system,  consisting  of  the  digestive,  excre- 
tory and  respiratory  organs ;  (4)  a  co-ordinating  and  reg- 
ulating  mechanism,    consisting   of   the   nervous    system, 
which  throws  the  different  motors  or  muscles  into  and  out 
of  action  at  the  times  needful  to  secure  the  results;  (5)  a 
protecting  and  insulating  system,  consisting  of  the  skin 
and  hair,  which  keeps  all  of  the  working  parts  free  from 
dust  and  reduces  the  waste  of  heat. 

606.  Muscles  Are  Motors. — Muscles  are  made  up  of  bun- 
dles of  fibers  which  can  be  stimulated  by  the  nervous  sys- 
tem and  made  to  shorten,  thus  exerting  a  pull  of  greater 
or  less  intensity  as  desired.     All  muscles  do  their  work  by 


488  Farm  Mechanics. 

shortening  and  a  pull  and  they  are  arranged  in  systems  of 
pairs  designed  to  produce  movements  in  opposite  direc- 
tions, as  illustrated  by  the  biceps  and  triceps  muscles  which 
move  the  fore  arm  as  represented  in  Fig.  234.  Just  how 
the  shortening  of  the  muscle  fibers  is  accomplished  under 
the  nervous  stimulus  sent  to  it  is  not  clearly  understood, 
but  it  is  known  that,  while  in  action,  the  muscle  fibers  are 
in  a  state  of  vibration  which  gives  rise  to  sounds  known  as 
the  muscular  murmur. 

When  muscles  are  in  action  and  are  producing  mechan- 
ical movements  their  temperature  changes  but  little,  but 
if  the  muscles  are  held  in  a  state  of  rigid  contraction  with- 
out producing  motion  as  the  result,  then  the  temperature 
rises,  showing  that  the  energy  which  normally  would  be 
changed  into  mechanical  motion  is  changed  into  heat ;  this 
is  exactly  what  occurs  in  a  steam  engine.  When  it  is 
working  hard  a  large  portion  of  the  heat  energy  of  the 
steam  is  transformed  into  mechanical  work  and  the  heat 
generated  in  the  fire  box  thus  disappears  but  the  moment 
the  engine  is  stopped  and  the  steam  is  held  so  that  it  is 
unable  to  produce  motion  of  the  piston  the  temperature 
rapidly  rises. 

607.  Strength  of  Muscles. — The  strength  of  individual 
muscles  is  often  very  great  and  more  than  at  first  seems 
possible.  Taking  the  case  of  the  biceps  and  triceps  mus- 
cles in  the  arm,  represented  in  Fig.  234,  it  is  possible  to 
measure  their  power  with  a  spring  balance.  If  a  loop  of 
strong  cord  is  fastened  to  each  end  of  a  spring  balance  and 
the  foot  put  through  one,  while  the  hand  is  put  through  the 
other,  the  strength  of  the  muscle  can  be  measured  by  lift- 
ing against  the  balance,  bending  the  fore  arm  so  as  to  make 
a  right  angle  with  the  arm  and  holding  it  horizontal  with 
the  elbow  against  the  edge  of  the  desk. 

A  man  of  average  strength  will  exert  a  pull  of  50  pounds 
in  this  way ;  and  as  the  lever  arm  upon  which  the  muscle 
acts  is  only  one-sixth  of  the  length  of  the  weight  arm  the 
pull  of  the  muscle  must  have  been  300  pounds.  When 


'Animals  as  Motors.  489 

the  strength  of  the  triceps  muscle  is  measured  in  a  similar 
way  it  is  found  to  be  able  to  exert  a  pull  of  25  to  30 
pounds ;  and  as  the  lengths  of  the  lever  arms  in  this  case 
are  in  the  ratio  of  1  to  20  or  1  to  24  the  power  of  the  mus- 
cle must  equal  500  to  600  pounds. 


f> 


FIG.  231.—  Showing  the  mechanical  action  of  muscles. 

It  is  clear  from  these  measurements  that  the  power  of 
the  larger  muscle^  in  a  horse  must  be  very  great  indeed. 

608.  Need  of  Great  Muscular  Strength.  —  It  is  because  the 
rate  at  which  muscles  are  able  to  change  their  length  is 
relatively  quite  slow  and  because  they  are  only  able  to  con- 
tract through  short  distances,  that  it  is  necessary  to  have 
them  act  upon  the  short  ends  of  levers  in  order  to  secure 
the  rapid  movements  through  long  distances  which  ani- 
mals are  obliged  to  make.     The  horse  as  an  engine  consists 
of  a  large  number  of  very  powerful  motors  acting  through 
a  system  of  levers. 

609.  Rate  at  Which  a  Horse  Can  Generate  Energy.  —  It  is 
recorded  in  (532)  that  about  the  maximum  walking  draft 
of  a  horse  is  one-half  his  own  weight  ;  pulling  with  this  in- 
tensity and  traveling  at  the  rate  of  2.5  miles  per  hour  the 
ability  of  a  1,600-pound  horse  would  be 

2.5X  5280  X  800 
60  X  60  X  550   =  5£  horse  power. 


490 


Farm  Mechanics. 


It  is  not  safe,  however,  to  have  a  horse  repeat  such 
strains  as  this  often  nor  maintain  them  long  at  a  time. 
Even  when  a  horse  is  pulling  with  an  intensity  of  one- 
fourth  its  weight  this  is  too  heavy  for  steady  work  and  rep- 
resents 

For  a  1,600-lb.  horse,  2f  H.  P. 

Foral,200-lb.  horse,  2    H.  P. 

For  a  1,000-lb.  horse,  If  H.  P. 

For  an  800-lb.  horse,  1£  H.  P. 

Indeed,  it  is  commonly  allowed  that  for  steady  and  con- 
tinuous work  10  hours  per  day  at  the  rate  of  2.5  miles  per 
hour  a  horse  should  not  be  asked  to  pull  more  than  \  to 
tV  of  its  own  weight.  At  this  rate  the  work  of  horses 
of  different  weights  would  be 

For  a  1,600-pound  horse,  1.06  to  1.33  H.  P. 

For  a  1,400-pound  horse,    .93  to  1.17  H.  P. 

For  a  1,200-pound  horse,    .80  to  1.00  H.  P. 

For  a  1,000-pound  horse,     .67  to    .83  H.  P. 

For  an   800-pound  horse,     .53  to    .67  H.  P. 

610.  Horse  Power  Required  to  Haul  Loads  on  a  Wagon — 
Taking  1  H.  P.  equal  to  550  foot-pounds  per  second  and 
the  data  in  the  table  of  (538),  the  number  of  horse  power 
required  to  haul  two  tons,  including  the  weight  of  the 
wagon,  under  the  conditions  there  stated,  are  given  in  the 
table  below : 

Table  giving  the  number  of  H.  P.  required  to  haul  2  tons  on 
wagons  under  different  conditions,  when  the  rate  of  travel 
is  2.5  miles  per  hour. 


Conditions. 

High 
wheels. 

Medium 
wheels. 

Low 
wheels. 

Dry  gravel  road;   sand  1  inch    deep;    some 
small,  loose  stones  

1.13 

1.21 

1.47 

Gravel  road  up  grade  i  in  44;  covered  with 
one-half  inch  wet  sand  ;  frozen  beneath  
Dirt   road    frozen;   thawing  one-half    inch; 
rather  rough  ;  mud  sticky  

1.64 
1.34 

1.76 
1.59 

2.31 

1  85 

Timothy  and  blue  grass  sod,  dry,  grass  cut.... 
Timothy  and  blue  grass  sod,  wet  and  spongy.. 
Cornfield,  flat  culture,  with  spring-tooth  cul- 
tivator ;  across  rows  •  dry  on  top  

1  76 

2.30 

2  38 

1.94 
2.70 

2  68 

2.38 
3.75 

3  55 

Plowed  ground  not  harrowed,  dry  and  cloddy. 

3  37 

4.23 

4.98 

Animals  as  Motors. 


491 


From  this  table  it  appears  that  the  hauling  of  two  tons 
on  a  wagon,  at  the  rate  of  2.5  miles  per  hour,  under  the 
varying  conditions  of  the  farm,  requires  a  team  to  develop 
energy  at  a  rate  ranging  from  1.13  H.  P.  to  as  high  as  4.98 
H.  P.  of  550  foot-pounds  per  second. 

611.  Horse  Power  Required  to  Plow. — Taking  the  draft 
of  the  stubble  plow  as  given  in  (305)  and  the  mean  rate 
of  travel  for  tli::  team  2.5  miles  per  hour,  the  mean  H.  P. 
required  t<.  do  the  work,  for  furrows  of  different  widths 
and  depth,  is  as  given  in  the  table  which  follows : 

Table  giving  the  H.  P.  required  to  draw  the  stubble  plow  when 
the  soil  is  in  medium  condition. 


Depth  of  furrow  

4  inches. 

5  inches. 

6  inches. 

7  inches. 

8  inches. 

Width  of  furrow  

10  inches. 

10  inches. 

10  inches. 

10  inches. 

10  inches. 

Horse  power  

1.44 

1.79 

2.15 

2.51 

2.87 

Wid  th  of  furrow  

12  inches. 

12  inches. 

12  inches 

12  inches. 

12  inches. 

Horse  power  

1.72 

2  14 

2.58 

3.02 

3.45 

Width  of  furrow  

14  inches. 

14  inches. 

14  inches. 

14  inches. 

14  inches. 

2.01 

2,51 

3.02 

3.52 

4.02 

From  this  table  and  the  one  of  (609)  it  appears  that  two 
1,600-pound  horses  find  their  full  capacity  for  work  taxed 
by  the  14-inch  plow  cutting  4  to  5  inches  deep ;  by  the  12- 
inch  plow  running  5  to  6  inches  deep  and  by  the  10-inch 
plow  running  6  to  7  inches  deep.  The  team  of  1,200- 
pound  horses  finds  its  full  ability  taxed  by  the  plow  cut- 
ting a  12-inch  furrow  4  to  5  inches  deep  and  a  10-inch  fur- 
row 5  to  G  inches  deep. 

612.  Increased  Speed  Diminishes  the  Traction  Power. — If 
the  horse  walks  more  rapidly  than  2.5  miles  per  hour,  or 
at  a  slower  pace,  the  force  which  he  can  exert  changes  also 
and  is  less  or  greater  than  100  pounds.  Experience  seems 
to  indicate  that  at  speeds  between  |  of  a  mile  and  4  miles 
per  hour,  and  continued  10  hours  per  day,  the  traction  will 
be  given  by  the  following  equation : 


492  Farm  Mechanics. 

2.5  miles  X  100  =  n  miles  X  Traction. 
Thus  at  two  miles  per  hour  the  traction  would  be: 

2.5  X  100  =  2  X  Traction, 
whence  Traction  =  2|Q  or  125  Ibs. 

613.  Diminishing  the  Number  of  Hours  Per  Day  Increases 
the  Power  of  Traction. — When  the  speed  remains  the  same 
experience  has  shown  that,  between  5  and  10  hours  per  day, 
diminishing  the  time  increases  the  possible  traction  in 
about  the  same  ratio,  or 

10  hours  X  100  =  n  hours  X.  Traction. 

Thus,  if  the  horse  is  to  be  worked  only  5  hours  the  trac- 
tion he  may  exert  will  be 

10  X  100  =  5  X  Traction, 
whence  Traction  =  *•*£*•  =  200  Ibs. 

PRINCIPLES   UNDERLYING  THE   DRAFT   OF   THE    HORSE. 

The  principles  governing  the  draft  of  a  wagon  have  been 
discussed  in  Chapter  XXj  there  are  others  affecting  the 
horse  as  a-  motor  which  need  to  be  considered  here. 

614.  Direction  of  the  Line  of  Draft. — When  a  horse  has 
a  muscular  development  and  a  type  of  skeleton  which  per- 
mits him  to  utilize  his  full  weight  in  hauling  then  the  di- 
rection of  the  line  of  draft,  or  of  the  traces  in  pulling,  ex- 
erts an  important  influence  upon  how  much  the  horse  can 
draw.     In  Fig.  235  is  represented  an  apparatus  for  dem- 
onstrating this  and  other  principles  underlying  the  draft 
of  the  horse. 

When  the  line  of  draft  is  horizontal,  as  represented  in 
the  figure,  the  spring  balance  will  register  a  tension  on  the 
traces  nearly  equal  to  the  weight  of  the  model  when  the 


Principles  Underlying  tlic  Draft  of  Hie  Horse.  49  ?> 

fore  feet  are  raised  from  the  ground,  and  this  is  the  limit 
of  its  power  to  draw  under  these  conditions.  If  the  traces 
are  moved  downward  it  is  clear  that  there  will  he  less  ten- 
dency to  tip  the  horse  up,  and  hence  the  greater  the  slope 
of  the  traces  the  more  will  be  required  to  raise  the  horse 
from  his  front  feet ;  and  at  an  angle  of  18  to  20  degrees  the 
weight  of  the  horse  will  permit  him  to  draw  double  what 
he  can  with  the  traces  horizontal.  If  the  traces  are  carried 
above  the  horizontal  then  the  horse  is  raised  from  his  front 
feet  more  easily  and  his  draft  will  be  decreased. 


Pro.  235.—  Apparatus  for  demonstrating  the  principles  of  draft  in  the  horse. 


It  is  difficult  to  get  a  living  horse  to  demonstrate  its 
full  ability  to  draw  in  a  standing  pull,  because  it  is  accus- 
tomed to  pull  against  loads  which  move.  In  the  case  of  a 
horse  weighing  1,645  Ibs.  a  measured  standing  draft  of 
1,250  Ibs.  has  been  recorded  when  the  traces  slanted  at  an 
angle  of  22°,  and  of  1,120  Ibs.  with  them  horizontal.  It  is 
doubtful  if  any  of  the  heavy  draft  horses  are  able  to  utilize 
their  full  weight  in  hauling  except  when  the  line  of  draft 
is  above  the  horizontal. 

615.  Influence  of  Weight  on  the  Draft  of  the  Horse.  — 
Weight  in  a  draft  horse  is  as  important  a  factor  to  his  ser- 


494  Farm  Mechanics. 

vice  as  it  is  in  a  locomotive ;  there  must  be  weight  enough 
to  make  a  secure  footing.  It  can  be  demonstrated  with 
the  apparatus  in  Fig.  235  that  two  pounds  at  the  place  of 
the  center  weight  in  the  figure  increases  the  ability  of  the 
model  to  draw  an  equal  amount  when  the  traces  are  hori- 
zontal and,  with  the  same  added  weight  and  the  traces 
given  a  slant  of  20  degrees,  the  ability  to  draw  is  increased 
4  pounds. 

These  results  mean  that  of  two  horses,  each  having  a 
muscular  power  capable  of  utilizing  its  full  weight,  the 
heavier  one  will  exert  the  stronger  pull.  The  1,200- 
pound  horse  may  pull  about  200  pounds  more  than  the 
1,000-pound  horse  of  like  build  when  the  traces  are  hori- 
zontal and  400  pounds  more  when  the  traces  slope  at  an 
angle  of  20  degrees. 

616.  Influence  of  the  Distribution  of  Weight  on  the  Draft 
of  a  Horse. — It  will  be  clear  from  an  inspection  of  the 
model  represented  in  Fig.  235  that  to  transfer  the  weight 
from  the  center  ring  to  the  forward  one,  giving  what  is  in 
effect  a  horse  with  heavier  shoulders,  will  make  the  weight 
count  for  more  in  preventing  the  horse  being  raised  off  his 
feet ;  so,  too,  will  it  be  evident  that  if  the  weight  is  shifted 
to  the  hind  quarters  it  must  have  much  less  influence  on 
the  draft. 

Indeed,  most  horses  in  heavy  draft,  when  given  the  free- 
dom of  the  head,  show  that  they  understand  this  principle 
in  practice,  by  both  lowering  the  neck  and  extending  the 
nose  forward,  thus  giving  this  portion  of  their  weight  a 
longer  leverage  to  hold  the  body  down  on  the  hind  feet 
which  are  acting  as  a  fulcrum. 

617.  Influence  of  the  Strength  of  the  Hock  Muscle  on  the 
Draft  of  a  Horse. — When  a  horse  is  drawing  a  heavy  load  a 
tremendous   strain   is    brought   upon   the  muscles   which 
straighten  the  hock  joint  so  as  to  force  the  body  forward, 
and  the  load  after  it,  in  walking;  and  it  is  a  deficiency 
of  ability  at  this  point  oftener  tha-n  at  any  other  which 
limits  the  power  of  the  horse  as  a  draft  animal. 


Principles  Underlying  the  Draft  of  the  Horse.    495 

With  the  spring  balance  represented  above  the  back  of 
the  model  in  Fig.  235,  which  controls  the  hinged  hock 
joint  through  a  rod,  it  is  possible  to  vary  the  tension  which 
holds  it  rigid  and  thus  demonstrate  the  ratio  of  muscular 
tension  to  the  draft  on  the  load  and  show  that  with  too 
weak  muscles  only  a  portion  of  the  weight  of  the  body  can 
be  utilized  in  draft.  In  the  model  the  tension  of  the  hock 
muscle  is  about  double  the  draft  and  while  this  is  not  in- 
tended to  demonstrate  the  relation  of  strength  of  muscle 
to  intensity  of  draft  in  any  horse  it  illustrates  the  funda- 
mental principle  and  shows  how  extremely  powerful  the 
muscles  of  the  horse  must  be  to  permit  him  to  make  the 
draft  he  does. 

618.  Influence  of  the  Width  of  the  Hock  on  the  Draft  of 
the  Horse. — JSTot  less  important  than  the  strength  of  the 
hock  muscle,  in  determining  the  qualities  of  a  draft  ani- 
mal, is  the  "width  of  the  hock  joint"  itself;  or,  stated  in 
the  language  of  mechanics,  the  ratio  between  the  two  arms 
of  the  lever  upon  which  the  hock  muscle  acts.  If  the  pro- 
jection of  the  heel  bone  backward,  which  forms  the  point 
of  the  hock,  is  long  in  comparison  with  the  distance  to  the 
hoof,  as  represented  in  the  diagram,  Fig.  236,  at  the  left, 
instead  of  short  as  shown  at  the  right,  then  it  is  clear  that 


FIG.  233. — Diagram  showing  difference  between  wide  and  narrow  hock. 

with  a  given  strength  of  hock  muscle  it  will  be  possible  to 
straighten  the  limb  under  a  greater  pull  and  the  ability  of 
the  horse  to  draw  is  thereby  increased.  In  the  model  rep- 


496  Farm  Mechanics. 

resented  in  Fig.  235  the  attachment  at  the  hock  joint  is  ar- 
ranged so  as  to  lengthen  the  power  arm  of  the  hock  muscle 
lever  different  amounts  and  thus  demonstrate  an  increas- 
ing draft  when  the  strength  of  the  muscle  is  maintained 
constant. 

In  fixing  the  attention  upon  the  hock  joint  as  influenc- 
ing the  draft  of  a  horse  it  is  not  intended  to  convey  the 
idea  that  other  features  are  not  important  or  that  they  do 
not  vary  in  a  marked  degree  in  the  different  types ;  for  it 
is  true  that  the  make-up  of  the  whole  body  of  the  draft  ani- 
mal is  notably  different  from  that  of  the  one  built  primar- 
ily for  speed,  but  the  type  of  variation  shown  at  the  hock 
joint  runs  through  the  whole  framework. 

619.  Attachment  of  the  Traces  to  the  Hames  at  the  Shoul- 
der.— To  enable  a  horse  to  utilize  his  full  weight  to  the 
best  advantage  in  draft  it  is  important  that  the  attachment 
of  the  traces  at  the  collar  should  be  as  low  as  the  comfort 
of  the  animal  and  other  conditions  will  permit.     When 
the  traces  are  low  at  the  shoulder  there  is  less  leverage  for 
the  draft  to  raise  the  horse  off  his  front  feet  and  hence  his 
weight  counts  for  more.     For  the  same  reason  a  horse  low 
on  his  feet  and  with  a  relatively  long  body  has  greater  lev- 
erage for  his  weight  in  draft. 

It  will  not  do  to  so  lengthen  the  hame  strap  above  and 
shorten  that  below  as  to  bring  the  attachment  of  the  traces 
down  upon  the  point  of  the  shoulder,  for  then  the  heavy 
pressure  of  the  collar  will  irritate  the  shoulder  and  make 
it  sore. 

620.  Two-Horse  Evener. — There  are  three  types  of  two- 
horse  equalizers  or  eveners  in  use  on  the  farm :  ( 1 )  where 
the  holes  for  the  whiffletrees  are  in  a  line  back  of  the  hole 
for  the  draft  pin;  (2)  where  the  holes  for  the  whiffletrees 
are  in  a  line  in  front  of  the  draft  pin;  and  (3)  where  all 
three  holes  are  in  the  same  straight  line. 

Each  of  these  types  of  evener  divide  the  work  equally 


Principles  Underlying  the  Draft  of  the  Horse.    497 

between  the  two  horses  so  long  as  the  evener  crosses  the 
line  of  draft  at  a  right  angle,  but  as  soon  as  one  horse  falls 
behind  the  other  then  only  the  third  type  remains  a  just 
equalizer.  The  truth  of  this  statement  can  be  readily 
demonstrated  with  the  apparatus  represented  in  Fig.  237, 
where  the  three  types  of  eveners  are  combined  in  one  piece. 


FIG.  237.  -Apparatus  for  demonstrating  the  principle'of  eveners. 


Referring  to  the  figure  it  will  be  seen  that  as  the  clevises 
for  the  whiffletrees  are  there  set  the  evener  may  be  made 
to  form  various  angles  with  the  line  of  draft  and  the  in- 
equality of  draft  resulting  may  be  measured  with  the  pair 
of  scales.  With  a  4-foot  evener  where  the  holes  for  the 
clevises  are  4  inches  behind  the  draft  pin  the  horse  which 
is  ahead  may  have  an  advantage  greater  than  25  per  cent., 
if  the  angle  formed  is  as  much  as  20°. 


498  Farm  Mechanics. 

Even  in  an  equalizer  where  the  three  holes  are  only  one 
inch  out  of  line  an  angle  of  20°  for  the  evener  with  tbe 
line  of  draft  may  give  the  horse  ahead  nearly  as  much  ad- 
vantage as  would  result  by  setting  the  clevis  of  the  other 
horse  in  toward  the  center  one  inch. 

When  the  holes  for  the  clevis  pins  are  in  front  of  the 
draft  pin  a  similar  inequality  of  division  of  labor  occurs, 
but  in  this  case  the  horse  which  is  in  front  must  pull  the 
most,  the  differences  measuring  as  great  as  with  the  other 
type.  When  the  three  pins  are  placed  in  a  straight  line 
there  is  nearly  a  true  division  of  labor  between  the  horses, 
even  when  the  angle  formed  by  the  evener  is  large.  This 
statement,  however,  is  only  true  when  the  clevis  pins  and 
the  draft  pin  fit  the  holes  closely. 

621.  Giving  One  Horse  the  Advantage. — When  it  is  de- 
sired that  one  horse  shall  do  more  work  than  the  other  this 
is  accomplished  by  shortening  the  lever  arm  of  the  horse 
which  it  is  intended  shall  do  the  larger  share  of  the  work. 
If  it  is  desired  that  the  off  horse  shall  do  60  per  cent  and 
the  near  horse  40  per  cent  of  the  work  then  the  clevis  pin 
of  the  off  horse  must  be  set  in  until  the  two  ends  of  the 
evener  are  in  the  reverse  ratio,  or  as  40  to  60. 

If  the  evener  is  48  inches  long  the  two  arms  would  be 
each  24  inches.  From  the  equation  of  the  lever  we  have 

PX  P A  =  WX  W A 
and  60  X  P  A  =  100  X  24 

whence  30  X  P  A  =  2, 400 

and  PA-  40 

From  this  is  appears  that  the  clevis  must  be  set  in 
48  —  40  =  8  inches, 

which  leaves  the  off  horse  with  a  weight  arm  of  16  inches 
and  the  near  horse  with  one  of  24  inches. 


Principles  Underlying  the  Draft  of  the  Horse.    499 


i,, —        -mm        — M 

PLOW  EVENERS.  flv£  HORSE  A8REAST' 

FIG.  238. — Equalizers  for  horses. 

622.  Three-Horse    Equalizer. — There    have    been   many 
forms  of  3-horse  equalizers  devised,  but  the  straight  bar  in 
which  one  horse  pulls  against  two 

others  is  the  simplest  and  gener- 
ally the  most  effective.  To  make 
this  evener  the  holes  should  all  be 
as  nearly  in  the  same  straight  line 
as  possible,  and  if  the  work  is  to  be 
divided  equally  the  hole  for  the 
draft  pin  should  be  placed  at  £  of 
the  length  of  the  evener  from  one 
end.  Fig.  238  represents  a  set  of 
three,  four  and  five-horse  equal- 
izers, and  Fig.  239  represents  a 
method  of  driving  four  horses 
abreast. 

nnn      nn         m         j    -n  mi       FIG.  239.— Ananpcment  of  lines 

623.  The    Tread    Power.    The   for  driving  four  horses  abreast. 

tread  power  is  a  rolling  end- 
less inclined  plane  so  arranged  that  its  motion  is  trans- 
ferred to  a  shaft  which  is  made  to  revolve  and  drive  a  belt. 
One  form  is  represented  in  the  upper  portion  of  Fig.  240, 
and  in  the  lower  portion  of  the  same  figure  are  represented 
two  forms  of  treads,  the  level  at  the  right  and  the  inclined 
at  the  left.  The  level  tread  has  the  advantage  of  permit- 
ting the  horse  to  travel  with  its  feet  more  nearly  in  the 


500  Farm  Mechanics. 

normal  attitude  to  its  limbs  and  on  this  account  the  fatigue 
is  supposed  to  be  and  probably  is  less. 


FIG.  240.— The  tread  power. 

In  order  that  a  large  per  cent  of  the  labor  expended  by 
the  horse,  when  working  on  the  tread  power,  shall  become 
available  it  is  very  important  to  have  all  of  the  bearings 
clean,  free  from  dust  and  grit  and  well  oiled.  There  are 
so  many  of  these  bearings  and  they  are  of  such  a  character 
that  great  care  is  required  in  running  this  power  to  avoid 
heavy  loss  of  efficiency  due  to  friction. 

624.  Working  the  Horse  in  the  Tread  Power — When  a 
horse  is  put  into  a  tread  power  to  work  he  accomplishes 
the  result  by  lifting  his  own  weight  against  the  force  of 
gravity  and  the  more  steeply  the  power  is  inclined  and 
the  faster  the  horses  walk  the  more  work  they  do.  Inclin- 
ing the  power  so  that  the  bed  rises  2  feet  in  8  feet  requires 
the  horse  to  lift  i  of  his  own  weight,  thus  producing  a 
pull  equal  to  that  on  the  belt  when  it  travels  at  the  same 
rate.  This  for  a  1,600-pound  horse  represents  a  pull  of 
400  Ibs. ;  for  a  1,200-pound  horse,  300  pounds ;  and  for  an 
800-pound  horse,  200  pounds.  If,  under  these  conditions, 
the  horse  walks  at  the  rate  of  2  miles  per  hour,  the  work 
done  will  be  2.13  H.  P.  for  the  1,600-pound  horse,  1.6 


Sweep  Power. 


501 


H.  P.  for  the  1,200,  and  1.07  H.  P.  for  the  800-pound 
horse.  These  results  are  about  double  the  horse  power 
for  corresponding  weights  where  the  draft  is  A  that  of 
the  weight  of  the  horse,  as  given  in  the  table  of  (609). 

It  is  a  common  practice  to  set  the  tread  power  as  steep 
as  2  feet  in  8  feet  and  when  this  is  done  it  is  clear  that  the 
horse  is  called  upon  to  develop  power  faster  than  he  is  able 
to  do  and  follow  it  day  after  day.  It  is  clear  also  how  a 
horse  may  be  made  to  do  more  work  in  a  tread  power  than 
when  drawing  on  the  sweep  power,  and  why  this  form  of 
power  may  appear  more  effective,  when  the  chief  differ- 
ence is  due  to  the  fact  that  the  horse  is  working  harder, 
and  horses  are  often  overworked  in  a  tread  power  without 
knowing  it  or  intending  to  do  so. 


FIG.  241.— The  sweep  power. 

625.  The  Sweep  Power — When  horses  are  worked  on  a 

sweep  power  such  as  is  represented  in  Fig.  241  it  is  im- 
32 


502  Farm  Mechanics. 

portant  that  the  line  of  draft  be  as  nearly  as  possible  at 
right  angles  to  the  sweep,  for  it  is  this  angle  .which  renders 
the  highest  per  cent,  of  the  draft  available.  It  will  be 
clear  from  the  upper  portion  of  the  figure,  representing  a 
plan  of  a  14-horse  sweep,  that  the  line  of  draft  there  can- 
not be  at  right  angles  to  the  sweeps  and  that  it  is  impossi- 
ble for  it  to  be  so  in  any  sweep  power.  On  this  account, 
there  is  a  considerable  portion  of  the  draft  lost  in  produc- 
ing pressure  on  the  bull-wheel  and  this  is  greater  the 
shorter  the  sweeps  are  and  the  longer  the  hitch  is  between 
the  horses  and  the  sweep.  If  the  line  of  draft  made  an 
angle  of  45  degrees  with  the  sweep,  one-half  of  the  power 
would  be  lost  in  pressure  on  the  bull-wheel  and  in  increas- 
ing the  friction. 

STEAM  ENGINES. 

The  steam  engine  is  one  of  the  earliest  of  man's  inven- 
tions designed  to  utilize  or  transform  molecular  motion, 
in  the  form  of  heat,  into  useful  work.  The  intense  vibra- 
tions which  are  caused  by  the  burning  fuel  in  the  combus- 
tion chamber  are  imparted  to  the  water,  converting  it  into 
steam  capable  of  exerting  greater  or  less  pressure,  accord- 
ing as  its  temperature  is  high  or  low. 

626.  Principle  of  Action  in  the  Steam  Engine. — It  was 
shown  in  (43)  that  966.6  heat  units  are  required  to  convert 
one  pound  of  water  at  212°  F.  into  steam  at  212°  under  a 
pressure  of  one  atmosphere;  and  in  (41)  it  is  shown  that 
these  heat  units  are  equivalent  to  752,305  foot-pounds  of 
work. 

The  fuel  value  of  one  pound  of  coal  is  14,000  heat  units 
which,  expressed  in  foot-pounds,  is 

14,000  X  778.3  =  10,896,200  foot-pounds. 

The  steam  engine  aims  to  utilize  the  power  of  coal  or  other 
fuel  by  transforming  its  enormous  potential  energy  into 


Steam  Engines.  503 

that  of  confined  steam,  and  if  it  were  only  possible  to  util- 
ize 80  or  90  per  cent,  of  this  power  the  steam  engine  would 
be  a  very  inexpensive  motor. 

627.  Efficiency  of  the  Steam  Engine. — It  is  unfortunately 
true  of  the  steam  engine  as  a  source  of  power,  that  in  prac- 
tical experience  it  is  only  able  to  render  available  from  2.5 
to  20  per  cent,  of  the  full  heat  value  of  the  fuel  burned  in 
the  fire  box,  and  it  is  still  more  unfortunate  that  there 
seems  to  be  little  hope  that  its  efficiency  can  ever  be  made 
to  much  exceed  31.5  per  cent.  The  reason  this  is  so  is  be- 
cause it  has  not  been  found  practicable  to  use  steam  at  very 
high  temperatures  nor  to  cool  it  much  below  that  of  the 
ordinary  air  conditions.  To  enable  a  water  wheel  to  util- 
ize the  highest  per  cent,  of  the  power  of  a  falling  stream  it 
must  be  so  arranged  as  to  be  able  to  take  the  water  at  the 
highest  possible  level  and  not  to  release  it  until  it  has 
reached  the  lowest  possible  level,  and  the  principle  is  the 
same  with  the  steam  engine.  If  the  steam  could  be  taken 
into  the  cylinder  at  a  temperature  of  1,000°  F.  and  re- 
leased from  it  only  after  its  temperature  had  fallen  to  60° 
F.  it  is  clear  that  much  more  work  could  be  performed 
than  when  the  temperature  is  only  permitted  to  fall  be- 
tween 300°  F.  and  212°  F. 

Where  heat  is  converted  into  work  the  efficiency  is  al- 
ways equal  to  the  quantity  of  heat  taken  into  the  engine 
minus  the  quantity  given  out  divided  by  the  quantity 
taken  in;  thus,  if  the  steam  entering  the  cylinder  carries 
100  heat  units  and  it  escapes  from  the  cylinder  with  90 
heat  units  after  moving  the  piston  the  efficiency  of  the  en- 
gine has  been  only 

100  —  90 

JQQ —    =  10  per  cent. 

So,  too,  if  steam  enters  a  cylinder  at  a  temperature  of  300° 
F.  and  escapes  at  212°  F.,  the  maximum  efficiency  would 
be  only 

(461  +  300)  -  (461  +  212) 

461  +  300  =  11 . 5  per  cent. 


504  Farm  Mechanics. 

In  this  equation  461  is  the  number  of  degrees  F.  which 
the  zero  of  the  Fahrenheit  scale  is  above  absolute  zero,  and 
in  such  problems  as  these  it  is  necessary  to  express  the  tem- 
perature in  absolute  degrees.  When  this  is  done  300°  F. 
becomes  761°  F  and  212°  F.  becomes  673°  F.,  and  the 
above  equation  becomes 

761  -  673 
— sgj =  11.5  per  cent. 

From  the  results  of  this  problem  it  is  clear  why  it  is 
not  possible  for  the  steam  engine  to  utilize  a  very  large  per 
cent,  of  the  total  energy  which  the  steam  carries  with  it 
into  the  cylinder.  Even  if  the  steam  could  be  carried  into 
the  cylinder  at  1,000°  F.  and  could  do  work  on  the  piston 
until  its  temperature  fell  to  100°,  the  maximum  efficiency 
would  only  be 

(1000  +  461)  —  (100  +  461) 

1000  +  461  61 ' 6  per  cent< 

628.  Pressure  of  Steam  at  Different  Temperatures. — The 
temperature  at  which  water  is  changed  from  a  liquid  into 
steam  or  invisible  vapor  varies  with  the  pressure  to  which 
the  water  is  subjected  as  stated  in  the  table  below: 

Table  showing  the  pressure  of  steam  or  water  vapor  at  differ- 
ent temperatures. 

Temperature  of  water.  Pressure  of  steam. 

102°  F 1  Ib.  per  sq.  inch. 

162       5  Ib.  per  sq.  inch. 

194       lOlb.  persq.  inch. 

212       14.73  persq.  inch. 

228       20  Ib.  per  sq.  inch. 

328       1(X)  Ib.  per  sq.  inch. 

432       350  )b.  per  sq.  inch. 

546       1000 Ib.  persq.  inch. 

629.  Dry   and   Wet   Steam. — When   steam   contains   no 
water  held  mechanically  in  suspension  it  is  known  as  dry 
steam,  but  it  is  seldom  possible  to  develop  absolutely  dry 
steam  because  as  it  escapes  from  the  surface  of  the  water 
in  the  boiler  there  is  a  tendency  to  carry  away  with  it 


Steam  Engines.  505 

more  or  less  water  in  the  form  of  tiny  drops,  such,  as  form 
the  white  cloud.  Steam  carrying  much  water  in  suspen- 
sion is  called  wet  steam. 

It  is  important  to  keep  this  property  of  steam  in  mind 
when  comparing  the  efficiency  both  of  boilers  and  of  en- 
gines. If,  for  example,  the  evaporating  surface  of  the 
water  in  the  boiler  is  small,  and  steam  is  forming  rapidly, 
so  that  large  quantities  of  water  are  carried  over  not  evap- 
orated, the  boiler  may  be  credited  with  evaporating  a 
large  amount  of  water  with  a  comparatively  small  amount 
of  fuel,  when  it  is  only  carrying  it  away  mechanically  sus- 
pended in  the  steam. 

Then,  too,  if  an  engine  is  being  worked  with  wet  instead 
of  dry  steam,  and  the  fact  is  not  known,  it  will  appear  that 
it  is  using  much  more  steam  for  a  given  amount  of  work 
than  it  really  is,  because  the  water  carried  over  in  this  way 
is  not  effective  in  developing  power. 

630.  Causes  of  Water  in  the  Cylinder  of  an  Engine. — 
There  are  several  causes  for  the  presence  of  water  in  the 
cylinder  of  an  engine,  and  these  may  be  stated  as — 

1.  Wetness  of  the  steam  coming  from  the  boiler. 

2.  Wetness  due  to  cooling  of  the  steam  when  passing 
through  pipes  and  steam  chest  on  its  way  from  the  boiler 
to  the  cylinder. 

3.  Condensation  of  steam  in  the  cylinder  when  the  en- 
gine is  first  started,  before  the  walls  become  heated  to  the 
temperature  of  the  steam. 

4.  Condensation  due  to  the  work   done   by   the  piston 
after  the  cut-off  has  occurred. 

5.  Condensation  due  to  cooling  of  the  walls  of  the  cylin- 
der itself. 

.  ...  ^     ...   ^ 

631.  Wetness  of  Steam  from  the  Boiler. — The  wetness  of 
the  steam  as  it  comes  from  the  boiler  is  modified  in  several 
ways:     (1)  If  the  steam  is  generated  rapidly  the  amount 
of  water  carried  over  is  larger  than  when  the  generation 
is  slow,  because  there  is  greater  mechanical  agitation.   (2) 


506  Farm  Mechanics. 

If  the  area  of  the  water  surface  at  the  water  level  in  the 
boiler  is  small  in  proportion  to  the  pounds  of  steam  deliv- 
ered the  water  carried  over  will  be  large  and  for  this  rea- 
son the  horizontal  boilers  of  a  given  H.  P.  tend  to  supply 
dryer  steam  than  the  vertical  boilers  do  because  there  is 
more  surface  from  which  the  steam  may  escape  and  the 
agitation  is  less.  (3)  If  the  volume  of  steam  space  above 
the  water  is  large  there  is  more  opportunity  for  the  sus- 
pended water  to  fall  back  and  leave  the  steam  dryer, 
hence  one  means  of  preventing  "priming,"  as  carrying 
over  water  is  called,  is  to  work  with  the  water  level  low 
in  the  gage  glass.  (4)  If  the  size  of  the  boiler  compared 
with  the  amount  of  steam  required  for  each  stroke  of  the 
piston  is  small  the  tendency  will  be  to  cause  the  pressure 
in  the  boiler  to  vary  and  this  variation  will  agitate  the 
water  and  cause  "priming."  When  this  is  the  case  prim- 
ing may  be  lessened  by  throttling  down  the  steam  supply 
at  the  stop  valve. 

632.  Wetness     Due    to    Condensation    in    Steam     Pipes 
and  Valve  Chest. — When  the  steam  pipes  are  long,  lead- 
ing from  the  boiler  to  the  steam  chest,  and  when  they  are 
not  jacketed  and  are  exposed  to  the  cold,  priming  is  pro- 
duced.    Jacketing  the  steam  pipes  and  the  steam  chest 
reduces  the  priming  from  this  cause  very  materially  be- 
cause   the  loss  of  steam  from  uncovered  iron  steam  pipes, 
per  degree  of  difference  of  temperature  between  steam  and 
outside  air,  is  about  2.4  heat  units  per  square  foot  of  out- 
side surface  of  the  pipe  per  hour,  while  covering  the  pipe 
with  wool  felt  one-half  an  inch  thick  reduces  the  loss  to  .7 
heat  units  in  the  same  time. 

633.  Initial  Condensation — The  temperature  of  the  walls 
of  the  cylinder  is  always,  in  practice,  colder  than   the 
entering  steam  as  it  comes  from  the  boiler  and  so  there 
must  be  a  greater  or  less  condensation  as  it  enters  until 
both  are  brought  to  the  same  temperature.     So  great  is 
tlio  condensation  of  steam  when  the  engine  is  first  started 


Steam  Engines. 


507 


that  it  is  necessary  to  provide  the  cylinder  with  relief 
cocks  at  each  end,  shown  at  8  in  Fig.  250,  which  must  be 
opened  at  the  start  to  allow  the  water  to  escape.  If  these 
are  not  opened  at  the  start  enough  water  may  collect  in  the 
cylinder  to  cause  the  piston  to  drive  out  the  head  of  the 
cylinder  or  do  some  other  injury. 

As  the  temperature  of  the  cylinder  gradually  increases 
less  and  less  water  is  deposited  and  then  the  relief  cocks 
may  be  closed,  the  water  which  is  condensed  afterward 
being  so  Jittle  that  it  is  re-evaporated  after  the  cut-off  takes 
place  and  during  the  exhaust  stroke  because,  as  the  piston 
travels,  the  space  for  the  steam  increases  and  this  reduces 
the  pressure  so  that  at  the  lower  pressure  the  heat  in  the 
walls  of  the  cylinder  is  able  to  re-evaporate  the  water 
which  had  been  condensed.  In  this  way  a  well  protected 
cylinder  keeps  itself  empty  after  it  has  become  heated. 

634.  Condensation  Due  to  Work  During  Expansion.- — 
When  the  steam  expands  and  expends  its  energy  in  driv- 


FIG.  243.— Horizontal  boiler. 


ing  the  piston  forward  its  temperature  is  lowered  in  pro- 
portion to  the  amount  of  work  which  it  does  and  on  this 


508 


Farm  Mechanics. 


account  more  or  less  of  water  tends  to  condense  in  the 
cylinder  which,  like  the  rest,  must  be  removed  by  re- 
evaporation. 

It  should  be  clear  from  this  and  the  preceding  para- 
graphs that  the  cylinder  should  be  well  jacketed  so  as 
to  reduce  as  far  as  possible  all  tendency  to  condense  the 
steam  in  the  cylinder  before  it  escapes  through  the  ex- 
haust. 

635.  Engine  Boilers — The  boilers  of  farm  engines  are 
commonly  one  or  the  other  of  two  types,  horizontal  or  up- 
right, represented  in  Figs.  243  and  244.  The  horizontal 
boilers  are  best  adapted  to  the  engines  of  the  larger  sizes 
"and  are  as  a  rule  the  most  economical  forms ;  but  where 
a  small  engine  is  desired,  and  especially  one  which  is 
compact  and  which  occupies  but  little  space,  then  the  up- 
right types  may  be  used,  such  as  represented  in  Fig.  244. 


FIG.  244.— Vertical  hotter  and  engine.' 


•Steam  Engines. 


509 


636.  Construction  of  Steam  Boilers. — Steam  boilers  are 
usually  made  of  strong  sheet  steel  f»  i  or  &  inches 
thick  which  are  rolled  into  cylindrical  forms,  securely 
riveted  and  often  braced  as  represented  in  Fig.  245.  The 
fire-box  is  placed  in  one  end  and  is  entirely  surrounded  by 
water  so  as  to  lessen  the  loss  of  heat.  The  boiler  repre- 
sented in  Fig.  245  is  designed  specially  for  burning  straw 
as  fuel,  which  is  introduced  into  the  fire-box  A,  from  which 
the  flame  passes  forward  through  the  main  large  flue  B 
into  the  combustion  chamber  C.  From  the  combustion 
chamber  the  flame  is  sub-divided,  returning  to  the  smoke 


FIG.  245.— Construction  of  steam  boiler. 

staek  E  through  the  small  flues  D.  In  the  same  figure 
FF  and  FF  represent  the  steam  dome  from  which  the  dry 
steam  is  taken  by  the  supply  pipe  G  to  the  steam  chest  at 
H,  not  represented.  At  the  bottom  of  the  boiler  at  KK 
and  -K.KKK  are  represented  hand  holes  to  be  used  in  clean- 
ing it  out.  The  construction  of  the  valve  for  closing 
the  hand  hole  is  shown  at  A  in  Fig.  243  and  also  the 
relation  of  the  flues  to  the  water  being  heated  by  them. 
In  the  arrangement  of  the  flues  in  the  boilers,  particular- 
ly in  the  horizontal  forms,  it  is  important  to  have  them 
placed  in  vertical  rows  rather  than  one  flue  above  the 
space  between  the  two  below,  in  order  that  there  may  be 
as  free  and  rapid  a  circulation  of  water  as  possible.  It  is 


510  Farm  Mechanics. 

very  important  in  the  construction  and  management  of  a 
boiler  to  so  arrange  conditions  as  to  have  as  little  difference 
of  temperature  in  all  parts  of  the  boiler  as  possible;  be- 
cause unequal  temperature  tends  to  develop  strains  in  the 
metal  and  to  tear  or  loosen  rivets  and  cause  leaks. 

637.  Gage  Cocks. — Boilers  are  commonly  provided  with 
three  gage  cocks,  represented  at  13,13  in  Fig.  244  and  at 
13  in  Fig.  249.     These  are  for  the  purpose  of  showing 
where  the  upper  surface  of  the  water  is  in  the  boiler  at 
any  time.     The  lower  gage  cock  is  placed  about  two  inches 
above  the  upper  surface  of  the  upper  flues  in  the  horizontal 
boiler. 

When  the  engine  is  running  the  water  is  held  in  the 
boiler  near  the  level  of  the  middle  gage  cock  and  is  fed 
into  the  boiler  so  as  to  reach  the  upper  gage  cock  only 
when  the  engine  is  to  be  shut  down  to  stand  for  some  time 
without  allowing  the  fire  to  go  out. 

638.  Gage  Glass.— The  object  of  the  gage  glass  is  to 
show  at  a  glance  just  what  the  water  level  in  the  boiler 
is  at  any  moment  and  its  position  is  represented  in  Figs. 
244  and  249  at  3. 

It  should  always  be  kept  in  mind  that  it  is  not  safe  to 
rely  entirely  upon  the  indications  of  the  gage  glass  be- 
cause it  is  peculiarly  liable  to  become  clogged  with  sedi- 
ment from  the  boiler ;  on  this  account  the  lower  cock  should 
be  frequently  opened  to  blow  it  off  and  clear  out  any 
sediment,  and  the  water  level  in  the  boiler  should  fre- 
quently be  tested  by  means  of  the  gage  cocks. 

When  the  engine  is  to  be  stopped  to  stand  with  the  fire 
on  for  any  length  of  time  the  gage  glass  should  be  closed, 
shutting  off  the  water  first  and  then  the  steam ;  this  is  to 
lessen  evaporation  and  to  prevent  escape  of  water  from  the 
boiler  in  case  the  gage  glass  should  break.  When  opening 
the  gage  again  the  steam  should  be  turned  on  first,  the 
water  last,  and  the  pet  cock  opened  to  blow  off  any  sedi- 
ment and  show  that  the  gage  is  in  proper  working  order 


Steam  Engines. 


511 


In  case  a  gage  glass  should  be  broken  when  the  pressure 
is  on  the  water  should  be  shut  off  first  and  then  the 
steam,  after  which  a  new  glass  may  be  put  in. 

639.  Pressure  Gage. — The  pressure  gage  is  intended  to 
show  the  number  of  pounds  per  square  inch  of  steam 
pressure  there  is  on  the  boiler  at  any  moment  and  to  serve 
as  an  indicator  to  the  fire- 
man of  the  condition  of 

his  fire.  It  is  represented 
at  4  in  Fig.  244  and  the 
interior  construction  of 
this  gage  is  shown  in  Pig. 
246. 

As  the  steam  enters  the 
hollow  spring  shown  in 
the  figure  its  pressure 
tends  to  straighten  it  be- 
cause the  pressure  on  the 
longer  circumference  is 
greater  than  that  On  the  FIG.  246.— Constmctioifof  steam  gage. 

shorter  one.     The  motion 

thus  produced  is  communicated,  through  a  segment  lever 
and  pinion,  to  the  index  which  is  made  to  revolve  over  a 
dial  upon  which  the  pressure  may  be  read. 

It  should  be  remembered  that  a  steam  gage  may  get 
out  of  order  and  fail  to  show  the  true  pressure.  In  such 
cases  the  operator  must  be  guided  by  the  safety  valve. 
(640).  Some  pressure  gages  are  provided  with  a  siphon 
placed  between  the  boiler  and  the  gage,  which  prevents 
the  dry  steam  entering  the  spring  at  too  high  a  tempera- 
ture and  also  automatically  drains  out  the  water,  thus 
preventing  injury  from  freezing. 

640.  Safety  Valve. — The  safety  valve  is  connected  with 
the  steam  chamber  of  the  boiler  where,  when  the  pressure 
reaches  a  point  as  high  as  the  boiler  is  intended  to  carry, 
it  may  be  opened  by  the  pressure  and  the  steam  be  allowed 


512 


Farm  Mechanics. 


to  escape,  thus  relieving  the  pressure  and  at  the  same  time 
warning  the  engineer  by  the  sound  of  the  escaping  steam. 
The  position  of  the  safety 
valve  is  represented  at  5,  Fig. 
244. 

Care  should  he  taken  hy 
the  operator  to  see  that  this 
valve  is  in  good  working  or- 
der by  raising  it  gently  at 
times  to  see  that  it  has  not  be- 
come set  in  some  way.  The 
weight  which  has  been  pro- 
vided by  the  manufacturers 
to  hold  the  valve  against  the 
steam  pressure  should  never 
be  made  heavier  by  loading 
or  so  set  that  it  will  oppose  a 
greater  pressure  than  the 
maximum  intended  for  the 
boiler. 

In  Fig.  247  is  represented 
the  Kunkle  lockup  pop  safety  valve  operated  by  a  spring 
instead  of  a  lever  and  weight. 

641.  Care  of  the  Boiler. — In  order  to  get  the  best  results 
from  a  boiler  it  is  necessary  that  the  flues  be  often  cleaned 
in  order  that  there  may  be  no  soot  or  ashes  to  prevent  the 
heat  coming  in  direct  contact  with  the  metal.  How  often 
this  should  be  done  must  depend  entirely  upon  circum- 
stances. Oftentimes  it  should  be  done  daily,  at  any  rate 
the  flues  should  be  kept  clean  and  the  draft  perfect. 

Periodically  it  is  necessary  to  clean  the  interior  of  the 
boiler  to  remove  the  scale  and  sediment  which  accumulates 
from  the  water  used  in  making  the  steam;  (649).  How 
often  this  must  be  done  will  depend  entirely  upon  the 
character  of  the  water.  In  some  cases  it  must  be  done 
once  a  week  but  with  clean  soft  water  it  may  not  be 
required  oftener  than  once  in  six  months. 


FIG.  247.— Kunkle  lockup  pop  safety 
valve. 


Steam  Engines.  513 

When  cleaning  is  to  be  done  it  is  important  to  make  sure 
that  the  fire  is  all  out  and  the  steam  should  be  permitted 
to  fall  to  as  low  as  10  pounds  before  the  blow-off  is  opened. 
If  the  fire  is  not  all  out  the  flues  may  be  made  to  leak 
and  if  the  steam  is  too  hot  the  mud  will  be  caked  on  the 
flues  so  that  it  cannot  be  readily  removed. 

In  replacing  the  plates  for  the  hand  holes  it  is  important 
to  see  that  they  are  clean  and  that  no  scale  or  dirt  is  on 
the  seat.  Sheet  lead  makes  the  best  packing  for  these 
places.  The  nuts  should  be  turned  up  tight  at  first  and 
after  steam  is  up  and  the  metal  expanded  they  may  need 
tightening  a  little  more. 

642.  Firing — Care  and  skill  are  required  to  do  good 
firing,  whether  with  wood  or  coal.  In  firing  with  wood 
it  is  necessary  to  keep  the  fire-box  nearly  full  all  the 
time  and  it  will  occasionally  require  "knocking  down" 
but  it  is  a  good  plan  not  to  use  the  poker  more  than  neces- 
sary. The  wood  should  be  placed  in  the  fire-box  as  closely 
as  practicable. 

In  firing  with  coal  the  grates  should  be  kept  as  evenly 
covered  as  possible  with  a  thin  fire,  avoiding  throwing 
on  large  lumps  of  coal  or  putting  on  large  quantities  at  a 
time.  If  the  coal  forms  clinkers  these  must  be  removed 
from  the  grate  through  the  door  but  it  is  desirable  not 
to  use  the  poker  when  it  can  be  avoided.  The  ashes 
must  be  kept  removed  form  under  the  grate  or  the  bars 
will  be  warped  or  melted. 

It  is  well  to  allow  the  safety  valve  to  blow  off  once  a 
day  to  note  how  this  and  the  pressure  gage  agree,  but 
good  firing  will  not  permit  this  to  occur  unless  the  engine 
is  stopped. 

When  the  fire  is  too  strong  it  may  be  controlled  by  open- 
ing the  door  to  the  fire-box  an  inch  or  less  or  leaving  the 
damper  open.  It  is  not  a  good  plan  to  open  the  fire  door 
and  close  the  damper  at  the  same  time  when  the  engine 
is  running. 

643,  Foaming. — Foaming  in  the  boiler  is  a  dangerous 


514:  Farm  Mechanics. 

symptom  and  should  be  avoided.  The  fact  is  indicated 
by  the  water  in  the  gage  glass  becoming  muddy  and  un- 
steady, rising  sometimes  very  high  and  then  falling 
again  as  quickly.  It  is  often  caused  by  dirty  water,  es- 
pecially when  it  contains  alkali  or  grease. 

When  foaming  occurs  it  is  difficult  to  tell  just  where 
the  water  stands  in  the  boiler  and  here  is  where  the  danger 
lies.  The  tendency  with  foaming  is  to  cause  the  heated 
surfaces  of  the  boiler  to  become  uncovered  and  become 
excessively  hot  so  that  when  the  water  returns  steam  may 
be  suddenly  generated  with  explosive  violence. 

644.  Low  Water  in  the  Boiler — If  by  any  chance  the 
water  should  become  too  low  in  the  boiler,  cool  judgment 
and  quick  action  are  called  for,  because  if  the  crown  sheet 
has  become  exposed  it  is  liable  to  be  weakened  by  over- 
heating.    In  short,  an  explosion  is  imminent.     The  thing 
to  do  first  is  to  cover  at  once  the  fire  in  the  fire-box  with 
three  or  four  inches  of  wet  ashes  or  earth  so  as  to  shut 
off  the  heat.     Do  not  under  any  circumstances  undertake 
to  rake  out  the  fire,  as  stirring  it  up  fresh  only  makes  the 
heat  more  intense  for  the  moment. 

At  such  a  time  the  safety  valve  should  not  be  opened  as 
the  sudden  release  of  pressure  which  this  would  permit 
may  cause  an  explosion  by  the  agitation  throwing  water 
onto  the  overheated  crown  plate.  The  thing  to  do  is  to 
allow  the  engine  to  cool  down  and  when  cool  enough  to 
refill  the  boiler. 

645.  Soft  Plug. — Boilers  are  provided  with  a  "soft  plug" 
which  screws  into  the  crown  plate  and  is  fitted  with  an 
alloy  which  melts  at  a  low  heat  to  allow  the  water  to  be 
forced  upon  the  fire  and  extinguish  it  before  the  crown 
sheet  could  be  injured.     Such  a  plug,  however,  is  not  al- 
ways reliable  as  the  top  of  it  may  become  coated  with 
lime  and  thus  rendered  ineffective.     On  this  account  the 
plug  should  be  removed  and  scraped  occasionally  and  it 
is  prudent  to  put  in  a  new  one  each  year  or  refill  it. 


Steam  Engines.  515 

If  a  soft  plug  blows  out  in  the  field  it  may  be  tem- 
porarily refilled  with  lead  or  Babbitt  metal  but  the  melt- 
ing point  of  these  is  too  high  to  prevent  the  plate  from 
being  injured.  The  soft  metal  is  an  alloy  made  by  melting 
together  equal  weights  of  lead  and  tin,  having  a  melting 
point  of  420°  F.,  that  of  lead  being  610°  and  Babbitt 
metal  650°  F. 

646.  Water  Supply. — The  water  supply  to  the  boiler 
must  always   be    adequate  and    under    complete    control. 
The  greatest  care    and  vigilance  should  be  exercised  by 
the  engineer  and  he  should  know  that  his  pump  and  in- 
jector are  in  prime  condition  at  all  times.     In  the  first 
place  the  cleanest  water  which  can  be  had  should  always 
be  used  and  if  necessary  the  water  should  be  strained  when 
it  is  put  into  the  supply  tank.     Be  sure  that  the  suction 
hose  and  connections  are  free  from  leaks.     It  sometimes 
happens  that  the  nipples  screwed  into  the  boiler  through 
which  the  injector  and  pump  feed,  lime  up  and  these 
should  be  examined  occasionally  to  see  that  they  are  free. 

There  are  two  methods  of  supplying  the  boiler  with 
water  (1)  with  a  pump  and  (2)  with  an  injector.  Pumps 
are  either  driven  by  the  engine  when  that  is  running  or 
directly  by  steam  pressure. 

647.  Cross-head  Pump. — A  common  form  of  pump  for 
supplying  the  boiler  with  water  is  known  as  the  cross- 
head  because  it  is  driven  from  the  cross-head  of  the  engine. 
This  being  true  it  is  of  course  only  available  when  the 
engine  is  running  and  an  engine  with  this  sort  of  pump 
should  also  be  provided  with  an  injector. 

The  independent  boiler  feed  pumps  are  some  one  of  the 
steam  types  and  are  practically  small  steam  engines  which 
drive  the  pump  cylinder. 

648.  The  Injector. — The  principle  by  which  steam  from 
the  boiler  is  able  to  force  water  back  into  the  same  boiler 
against  the  same  pressure  and  the  action  of  the  injector 


516 


Farm  Mechanics. 


is  as  follows:  When  steam  is  issuing  from  the  boiler 
under  a  pressure  of  eighty  pounds  and  entering  the  in- 
jector at  V,  Fig.  248,  it  may  have  a  velocity  of  nearly 
1,800  feet  per  second;  as  this  passes  through  E  into  S 
it  produces  a  strong  suction  in  through  the  suppl-y  pipe 
and  when  the  steam  strikes  the  cold  water  it  is  at  once 
condensed.  But  when  the  steam  is  condensed  into  water 
it  still  has  its  high  initial  velocity  and,  striking  the  incom- 
ing water,  drives  a  portion  of  it  directly  into  the  mouth  Y 
through  into  the  chamber  O  and  from  thence  into  the 
boiler. 


FIG.  248.— Penberthy  injector. 


When  the  injector  is  used  at  a  steam  pressure  of  65 
pounds  the  water  supply  valve  is  opened  one  turn,  then 
the  steam  valve  wide.  If  the  injector  does  not  start 
at  once,  and  water  runs  from  the  overflow,  throttle  the 
water  supply  slowly  until  it  picks  up ;  but  if  hot  steam  and 
water  issue  from  the  overflow  open  the  water  supply  valve 
farther. 


Steam  Engines.  517 

649.  Boiler  Incrustation — The  use  of  hard  water  for 
making  steam  results  in  the  precipitation  of  the  carbonates 
of  lime  and  magnesia,  and  their  sulphates  also,  when  these 
are  present,  on  the  flues  and  walls  of  the  boiler  in  the  form 
of  a  more  or  less  resistant  scale  which  may  be  harmful  in 
several  ways:  (1)  The  incrustation  on  the  boiler  is  not 
a  good  conductor  of  heat  and  both  the  capacity  and  effi- 
ciency of  the  boiler  are  decreased.  (2)  When  a  heavy 
crust  forms  on  the  boiler  which  prevents  perfect  contact 
of  the  water  the  boiler  may  become  overheated  and  the 
scale  thus  weaken  it  by  allowing  it  to  "burn  out."  (3)  It 
is  thought  that  even  boiler  explosions  may  sometimes  orig- 
inate from  the  thick  scale  suddenly  flaking  off  when  the 
boiler  underneath  is  overheated  and  thus  letting  the  hot 
water  come  suddenly  in  contact  with  the  hot  surface,  which 
results  in  the  sudden  evolution  of  a  large  volume  of  steam. 

To  prevent  the  formation  of  scale  on  boilers  and  to,  re- 
move it  when  formed  many  methods  have  been  proposed. 
A  common  one  is  to  use  the  simple  sodium  carbonate  or 
sal  soda  of  commerce,  dissolving  a  quantity  in  water  and 
letting  it  be  fed  into  the  boiler  with  the  water.  Its  action 
is  to  cause  the  carbonates  to  be  precipitated  in  a  more  or 
less  powdery  form  which  does  not  adhere  to  the  flues  so 
firmly.  It  is  possible  that  the  influence  of  the  sodium 
carbonate,  besides  taking  up  the  excess  of  carbon  dioxide 
from  the  bicarbonates  of  lime  and  magnesia,  is  to  floc- 
culate the  lime  and  magnesium  carbonates  and  sul- 
phates, causing  them  to  fall  in  larger  granules  which 
have  not  the  power  of  adhering  to  the  walls  of  the 
boiler  and  flues  as  the  molecules  do.  Sometimes  ammoni- 
um chloride  is  used  and  in  this  case  the  carbonates  are 
converted  into  chlorides,  which  are  very  soluble  in  the 
water,  while  the  ammonium  carbonate  is  volatile  and 
passes  off  with  the  steam.  Where  the  steam  is  not  to  be 
used  for  any  other  purpose  than  driving  the  engine,  kero- 
sene is  sometimes  employed  but  its  method  of  action  is 
not  clearly  understood. 
33 


518 


Farm  Mechanics. 


650.  The  Engine. — Most  farm  engines  are  mounted  upon 
their  boilers  as  represented  in  Fig.  244,  at  the  left,  and 
in  Figs.  249  and  250.  Its  chief  parts  are  the  cylinder,  5 ; 
the  steam  chest  with  sliding  valve,  4;  the  fly-wheel,  2; 
the  eccentric ;  the  governor,  6 ;  and  the  throttle  valve,  7. 

The  construction  of  the  cylinder  of  the  compound  en- 
gine is  shown  in  Fig.  252,  where  A  is  the  high  pressure  cyl- 
inder, B  the  low  pressure  cylinder  and  1,  1,  1,  1,  1,  1,  1,  1, 
the  sliding  valve  which  regulates  the  entrance  and  exit  of 


FIG.  249.— Portable  steam  engine . 

the  steam.  As  the  steam  from  the  boiler  comes  to  the  steam 
chest  at  E  it  first  enters  the  compartment  D  of  the  slide 
valve  by  a  port  not  shown  in  the  section  and  from  there  is 
conveyed  into  the  cylinder  A  along  the  passage  O  where  it 
forces  the  piston  toward  G.  While  this  is  being  done  the 
steam  on  the  other  side  of  the  piston  at  A,  which  has 
spent  only  a  part  of  its  energy,  passes  out  through  the 
passage  2,2,  into  the  steam  chest  C  from  which  it  enters 
the  large  cylinder  B  on  the  side  of  the  piston  at  3  and 


Steam  Engines. 


519 


FIG.  250.— Portable  steam  engine. 

in  this  position  assists  the  high  pressure  steam  in  driving 
the  piston  toward  G.  On  the  opposite  side  of  the  large 
piston,  in  the  low  pressure  cylinder  B,  is  the  steam  which 
has  spent  its  available  energy  in  driving  the  large  piston  in 
the  opposite  direction  and  this  is  being 
forced  out  through  the  passage  4,4  into 
the  exhaust  5.  At  the  proper  time,  when 
the  pistons  are  nearing  the  ends  of  the 
cylinders  toward  G,  the  eccentric  reverses 
the  action  of  the  rod  F  and  pushes  the 
slide  valve  until  6  stands  over  4  and  7 
over  2,  which  permits  the  high  pressure 
steam  to  enter  A'  through  2,2  and  the  811 
partly  expanded  steam  to  enter  B  by  way 
of  O  to  C  and  from  thence  through  4,4  to 
B,  when  the  direction  of  motion  of  the  pis- 
ton is  reversed. 

mi  .„,.,,   FIG.  251.— Piston  head 

Ihe   construction   of  the    piston    head  with  metal  packing, 
with  its  self  adjusting  metal  packing  rings 
are  shown  in  Fig.  251. 


520 


'Farm  Mechanics. 


Steam  Engines. 


521 


FIG.  253.— Governor  of  steam  engine. 


651.  Governor. — In  order  that  the  speed  of  the  engine 
may  be  controlled  it  is  necessary  that  the  amount  of  steam 
admitted    to    the    cylinder 

should  vary  with  the  work 
before  the  engine.  To  main- 
tain a  uniform  speed  there 
is  provided  a  governor,  one 
form  of  which  is  represented 
in  Fig.  253,  whose  action  is 
as  follows : 

At  the  point  2  in  the  pipe 
1  leading  from  the  boiler 
there  is  a  valve  which  can  be 
opened  and  closed  by  the  ac- 
tion of  the  balls  4,  which 
are  made  to  revolve  by  the 
belt  working  on  the  pulley 
3.  As  the  speed  of  the  en- 
gine increases  the  balls  of 
the  governor  are  made  to  revolve  more  rapidly  and  by  their 
centrifugal  force  bend  the  strips  of  elastic  metal  to  which 
they  are  attached  outward,  and  this  draws  the  upper  end 
of  the  spindle  downward,  partly  closing  the  valve  at  2.  By 
means  of  the  spring  at  5  the  resistance  the  governor  must 
overcome  to  close  the  valve  may  be  varied  and  in  this  way 
the  governor  may  be  set  so  as  to  cause  the  engine  to  run 
steadily  at  different  speeds. 

652.  Lubricator. — To  keep  the  valves  in  the  steam  chest 
and  the  cylinder  well  oiled,  a  special  form  of  lubricator  is 
required,  and  one  of  these  is  represented  in  Fig.  254  and 
is  seen  in  place  on  the  engine  at  10,  Fig.  249.     This  is 
screwed  into  the  steam  pipe  leading  to  the  steam  chest  at 
the  threaded  end  H.     The  oil  receptical  is  the  cylinder 
above  I  which  must  be  filled  bv  removing  F,  but  first  clos- 
ing E  and  G  and  removing  I  so  as  to  drain  out  the  water. 
After  returning  I  the  oil  cup  is  filled  entirely  full  above 
the  level  of  the  sight-feed  D,  when  F  is  again  closed  and 
E  and  G  opened. 


522 


Farm  Mechanics. 


The  action  of  the  lubricator  is  caused  by  steam  rising 
into  the  bend  B  and  condensing  in  the  left  leg.  The  water 
being  heavier  than  oil 
flows  through  G  across  the 
glass  face  D  and  falls  to 
the  bottom  of  the  oil  reser- 
voir, thus  forcing  a  like 
amount  of  oil  up  and  out 
through  valve  E  and  on 
into  the  steam  pipe  where 
the  steam  carries  it  into  the 
steam  chest  and  cylinders. 
When  the  oil  is  all  out  of 
the  cup  the  water  shows 
through  the  face  D,  and  the 
lubricator  must  be  refilled. 


D 


I 


FIG.  254.— Swift  sight  feed  lubricator. 


653.  FlyWheel.— In  all 

single  crank  engines  it  is 
very  important  to  have  a 
well  designed  and  ample 
fly  wheel  in  order  to  en- 
sure steady  running  of  the 
engine.  It  will  be  clear 

that  as  the  piston  rod  passes  through  the  course  of  its 
stroke  its  efficiency  must  rise  and  fall  as  it  approaches 
and  recedes  from  the  dead  centers.  The  fly  wheel,  repre- 
sented at  2  in  Figs.  244,  249  and  250,  enables  energy  to 
be  stored  in  its  heavy  fast-moving  rim  when  the  crank  shaft 
has  the  greatest  efficiency  and  this  may  be  given  out  again 
to  maintain  the  speed  when  the  dead  centers  are  being  ap- 
proached and  passed. 

GASOLINE  ENGINES. 

Within  the  past  ten  years  there  has  been  a  strong  move- 
ment to  place  upon  the  market  for  farm  use  motors  of  the 
internal  combustion  type  and  many  kinds  of  gasoline  en- 


Gasoline  Engines.  523 

gines^  ranging  from'  1  to  15  and  20  horse-power,  are  now 
offered  for  sale  by  manufacturers.  While  it  cannot  be 
said  that  these  motors  have  in  general  earned  for  them- 
selves the  reputation  for  reliability  that  steam  engines  pos- 
sess, it  is  now  acknowledged  that  there  are  upon  the  mar- 
ket gasoline  engines  which  are  efficient  and  quite  satisfac- 
tory for  farm  purposes. 

654.  Gasoline  and  Steam  Engines  Contrasted. — Gasoline 
engines   are   widely   different   from  the   steam   types  de- 
scribed in  the  last  section.     In  those  the  power  is  derived 
from  a  steadily  burning  fire  converting  water  into  steam, 
which  transmits  the  power  to  the  working  parts  of  the  en- 
gine; in  these  the  fire  is  an  intermittent  one  which  is  al- 
most instantaneous  in  duration  and  which  begins  and  ends 
like  an  explosion.     Indeed,  the  gasoline  engine  may  be 
likened  to  a  cannon  which  loads  and  fires  itself  at  deter- 
mined intervals  and  where  the  ball  is  a  piston  whose  mo- 
tion is  arrested  by  a  crank  shaft  and  transformed  into  rot- 
ary motion  in  the  fly  wheels  of  the  engine,  to  be  used  as  a 
source  of  power.     After  the  first  charge  has  been  fired  a 
portion  of  its  energy  is  used  to  reload  the  piece  again, 
making  it  ready  for  a  second  explosion,  to  be  repeated  as 
often  as  needed. 

655.  Principal  Parts  of  a  Gasoline  Engine. — The  gasoline 
engine,  like  the  steam  engine,  has  its  cylinder  and  piston, 
and  its  fly  wheel  and  governor,  but  it  has  no  boiler  or  fire- 
box and  is  much  more  simple  in  its  construction  and  man- 
agement.    There  are  provisions  for  supplying  the  engine 
with  gasoline  and  air  as  needed  for  the  explosions,  for  ig- 
niting the  charge  when  ready  and  for  disposing  of  the 
waste  products  after  the  explosion  has  taken  place. 

656.  The  Working  Cycle. — The  working  cycle  of  moat 
gasoline  engines  consists  of  five  operations : 

1.  Charging  the  cylinder  with  the  explosive  mixture  of 
air  and  gasoline  vapor. 


624  Farm  Mechanics. 

2.  Compressing  the  charge  preparatory  to  explosion. 

3.  Igniting  the  compressed  charge. 

4.  Expansion  of  the  charge  after  its  explosion. 

5.  Expulsion  of  the  waste  products  of  the  explosion. 

657.  Arrangements  to  Prevent  Over-heating. — The  con- 
tinual repetition  of  the  explosions  in  the  cylinder  of  the 
engine  results  in  so  much  heating  of  the  parts,  where  any 
considerable  work  is  done,  that  it  is  found  necessary  to 
provide  means  for  absorbing  the  heat  not  changed  into  me- 
chanical motion.  This  is  usually  done  by  providing  the 
working  parts  which  come  in  contact  with  the  heat  with 
water  jackets  in  which  water  or  oil  is  kept  circulating  to 
absorb  the  heat  imparted  to  them. 

Where  water  is  used  to  cool  with  it  is  necessary  in  freez- 
ing weather  to  draw  it  off  when  the  engine  is  shut  down  to 
avoid  injury,  but  where  a  lubricating  oil  is  used  as  the  cir- 
culating medium  there  is  no  danger  of  this  sort. 


FIG.  255.— Horizontal  gasoline  engine . 

658.  Types  of  Gasoline  Engines. — Gasoline  engines,  like 
the  boilers  of  steam  engines,  are  spoken  of  as  vertical  or 
horizontal  according  as  the  cylinder  is  upright  or  horizon- 
tal. It  is  possible  to  make  the  floor  space  occupied  by  the 
upright  engines  less  than  with  the  horizontal  forms,  but 
with  few  exceptions  all  the  larger  engines  belong  to  the 


Construction  of  the  Gasoline  Engine.  525 

horizontal  type.     These  two  types  of  engines  are  repre- 
sented in  Figs.  255  and  256. 


CONSTRUCTION  OF  THE  GASOLINE  ENGINE. 

659.  Cylinder — The  cylinder  of  the  ordinary  gasoline 
engine  with  its  piston  is  not  widely  different  from  that  of 
the  steam  engine,  except  that  here  there  is  nothing  which 
corresponds  to  the  steam  chest  and  the  slide  valve,  and  the 
cylinder  has  a  double  jacket  through  which  water  is  kept 
circulating  to  prevent  over-heating.     In  Fig.  255  A  repre- 
sents the  cylinder  and  the  opening  on  the  side  is  the  ex- 
haust port. 

The  piston  has  essentially  the  same  construction  as  that 
of  the  steam  engine  represented  in  Fig.  251,  using  similar 
elastic  metallic  packing  rings.  There  being  no  head  in  one 
end  of  the  cylinder  the  piston  can  usually  be  seen. 

660.  Pumping  Mechanism — Formally  it  was  the  practice 
to  arrange  the  gasoline  supply  tank  so  that  the  oil  would 
How  by  gravity  to  the  engine,  but  this  practical  experience 
has  proved  to  be  unsafe  on  account  of  the  tendency  for 
leaks  to  develop  and  flood  the  engine  room  with  the  explo- 
sive oil.     The  plan  now  generally  followed  is  to  use  an 
automatic  pump,  represented  in  connection  with  the  en- 
gine in  Fig.  257,  where  D  is  the  plunger  and  A,  B,  C  parts 
for  working  it  when  it  is  desired  to  throw  a  charge  into  the 
reservoir  H.     The  gasoline  comes  from  a  tank  outside  the 
building  through  the  valve  F,  and  is  discharged  from  the 
pump  through  the  pipe  E  into  H. 

The  disk  with  the  hand  wheel  J  is  used  to  regulate  the 
amount  of  oil  going  to  the  engine  and  when  the  pointer  I 
is  over  the  letter  O  the  valve  is  wide  open,  but  the  proper 
amount  of  oil  is  supplied  when  the  pointer  is  at  R  in  this 
engine.  The  air  is  drawn  in  through  the  same  chamber 
H  by  means  of  a  pipe  not  shown  in  the  cut,  which  ends  un- 
der the  base  of  the  engine  where  as  little  dust  as  possible 
will  be  sucked  in. 


526 


Farm  Mechanics. 


661.  Governor. — The   governing    mechanism    for   gaso- 
line engines  varies  in  detail,  but  is  usually  a  device  by 


FIG.  256.— Vertical  gasoline  engine  showing  governing  mechanism. 

which  the  pump  is  made  to  supply  a  charge  of  gasoline 
whenever  an  explosion  is  desired  and  the  essential  parts 
of  the  mechanism  are  represented  in  Fig.  256,  where  E  E 
are  a  pair  of  governing  balls  which  revolve  with  the  fly- 


Construction  of  the  Gasoline  Engine.          527 

wheel  and  operate  a  finger  in  such  a  way  as  to  prevent  a 
charge  being  given  to  the  engine  whenever  its  speed  is 
running  too  high.  As  the  speed  runs  up  the  balls  fly 
apart  and  this  brings  the  finger  C  down  upon  the  catch  B 


FIG.  257. — Pumping  mechanism  for  supplying  gasoline  to  gasoline  engine. 

which  holds  the  exhaust  valve  open  and  prevents  the  pump 
being  worked.     The  catch  and  finger  are  more  clearly  seen 


528 


Farm  Mechanics. 


at  M  in  Fig.  257  where  the  upper  K  is  the  valve  stem 
which  also  works  the  gasoline  pump. 

662.  Valve  Mechanism. — The  supply  and  exhaust  valves 
for  the  engine  of  Fig.  256  are  represented  in  Fig.  258  and 


FIG.  258.— Valve  mechanism  of  gasoline  engine. 

are  located  in  the  chamber  A  of  Fig.  256.  The  upper 
valve  A  is  the  exhaust  and  is  represented  forced  down  so 
as  to  open  the  port,  allowing  the  burnt  charge  to  escape  up- 


Construction  of  the  Gasoline  Engine.       529 

ward  to  reach  the  opening  E  in  Fig.  258,  which  is  the 
same  as  F  in  Fig.  256.  When  this  valve  is  closed  it  is  at 
H  and  is  always  controlled  by  the  stem  C  worked  by  the 
revolutions  of  the  fly-wheels. 

The  supply  valve  B  is  represented  closed  and  is  held 
down  by  the  spring  K,  which  can  be  regulated  by  the  ten- 
sion given  through  the  jamb-nut  L.  This  valve  is  lifted 
by  the  suction  produced  by  the  up-stroke  of  the  engine  pis- 
ton. The  opening  G  is  a  water  jacket  around  the  valves 
to  keep  them  cool. 

663.  Igniting  the  Charge. — There  are  two  methods  of  ig- 
niting the  charge  at  the  proper  time,  in  these  engines :  one 
is  by  means  of  an  electric  spark  which  is  produced  at  just 
the  right  time  by  means  of  a  devise  worked  by  the  engine ; 
the  other  is  by  means  of  a  hot  tube  which  rises  out  of  the 
chamber  A,  of  Fig.  256,  into  the  curved  chimney  standing 
just  to  the  left  of  C  B.     This  tube  is  kept  at  the  proper 
temperature  by  means  of  a  Bunsen  burner  fed  through  the 
cock  shown  above  F  and  at  L,  Fig.  257.     After  the  charge 
has  been  drawrn  in  and  the  piston  is  coming  down  in  the 
cylinder  so  as  to  compress  the  gas,  this  compression  forces 
a  part  of  the  explosive  mixture  up  into  this  hot  tube  and 
when  this  is  done  the  gas  ignites  and  an  explosion  follows. 
If  this  tube  becomes  too  hot  the  tendency  will  be  for  it  to 
explode  the  charge  too  soon  and  either  lessen  the  power  of 
the  engine  or  reverse  its  motion.     If  it  is  too  cold  the  ex- 
plosion will  be  too  late.     After  the  tube  has  been  used  for 
some  time  a  scale  may  form  over  it  which  prevents  the  in- 
ner wall  from  taking  the  proper  temperature  and  it  is  then 
necessary  to  replace  it  with  a  new  one.     In  replacing  this 
tube  it  is  necessary  to  use  one  which  is  adapted  specially 
to  the  engine  because  if  it  is  too  large  or  too  small,  or  too 
long  or  too  short,  its  capacity  will  affect  the  time  of  the 
explosion  and  it  will  not  be  correct. 

664.  Lubrication — Cleanliness  of  all  working  parts  of 
the  engine  and  proper  oiling  are  matters  of  prime  impor- 


530  Farm  Mechanics. 

tance  and  should  receive  the  most  careful  attention.  It 
requires  a  special  lubricating  oil  for  gasoline  engines  and 
only  this  oil  should  be  used.  It  is  known  on  the  market 
as  gas  or  gasoline  engine  oil.  All  parts  should  be  care- 
fully wiped  clean  at  frequent  intervals  to  free  them  from 
grit  or  gummy  products  and  the  operator  should  uhvavs 
have  an  ear  to  the  sounds  of  his  engine  and  should  know 
what  are  normal  and  what  are  not  in  order  that  he  may 
the  quicker  discover  when  anything  is  getting  out  of  order 
and  remedy  it  in  time. 

665.  Gasoline. — Only  the  best  quality  of  gasoline  should 
be  used  with  these  engines,  that  known,  as  the  "74°  test 
gasoline." 

666.  Size  of  Engine — In  purchasing  a  motor  of  any  kind 
it  should  be  remembered  that  it  is  much  better  to  get  one 
which  has  a  little  greater  capacity  than  will  be  needed 
than  one  which  is  a  little  too  small ;  and  this  caution  ap- 
plies with  special  force  to  the  gasoline  engines,  for  the  rea- 
son that  their  capacity  cannot  be  increased  above  the  nor- 
mal.    With  the  steam  engine  it  is  possible  to  increase  the 
steam  pressure  and  the  rate  of  firing,  and  the  horse  may 
for  a  short  time  develop  two,  three  or  even  four  horse- 
power, but  if  you  overload  a  gasoline  engine  it  must  stop. 
If,  therefore,  it  is  desired  to  use  steadily  two  full  horse- 
power from  a  gasoline  engine  it  should  be  not  less  than  a 
three  horse  actual  to  do  at  all  times  perfectly  satisfactory 
work. 

It  should  be  said  in  this  connection,  however,  that  it  is 
never  economical  of  fuel  to  use  a  large  engine  to  develop  a 
small  horse-power.  A  10  H.  P.  engine  could  not  be  eco- 
nomically used  when  it  is  desired  to  simply  pump  water 
from  an  ordinary  well  or  to  run  a  small  separator  which  a 
man  can  turn.  There  should  be  a  rational  relation  be- 
tween the  engine  and  the  amount  of  work  it  is  expected 
to  perform, 


Windmill  531 


WINDMILL. 

If  we  except  horse-power  and  that  of  cattle  there  is  no 
form  of  motor  which  has  been  so  generally  or  so  widely 
used  on  the  farm  as  the  windmill  and  its  use  is  daily  in- 
creasing, especially  now  since  all  parts  are  made  of  steel 
well  galvanized  to  protect  them  from  rust,  and  their  rela- 
tive efficiency  has  been  increased. 

667.  Work  to  Which  the  Windmill  Is  Adapted. — It  must 
not  be  understood  that  a  windmill  is  well  suited  to  furnish 
power  for  any  and  all  kinds  of  farm  work  if  only  it  is 
made  large  enough.  On  the  contrary  it  is  only  adapted 
to  certain  lines  where  the  work  done  can  be  accumulated 
at  times  when  the  wind  is  favorable. 

The  windmill  is  peculiarly  well  adapted  to  pumping 
water  for  stock  and  for  the  supply  of  the  house  if  only  a 
suitably  placed  reservoir  of  sufficient  capacity  is  provided. 
It  must  be  remembered,  however,  that  in  many  localities 
there  may  be  periods  of  calm  of  three  or  even  occasionally 
of  seven  days'  duration  when  there  will  not  be  wind  enough 
to  permit  the  mill  to  do  any  work. 

For  grinding  grain  for  farm  stock  the  windmill  is  pecu- 
liarly well  suited,  provided  arrangements  are  made  so  that 
the  grinder  is  automatically  fed  and  the  meal  "allowed  to 
drop  into  a  bin  where  it  may  accumulate  without  personal 
attention.  Arrangements  of  this  sort  may  easily  be  made 
but  it  requires  a  special  form  of  grinder  which  is  not  only 
automatic  in  its  feed,  but  in  the  rate  at  which  it  feeds  as 
well,  supplying  the  mill  heavily  when  the  wind  is  strong 
and  leaving  the  burrs  empty  whenever  the  wind  falls  so 
that  no  work  can  be  done. 

Where  an  abundance  of  water  is  available,  with  a  lift  of 
only  10  to  20  feet,  the  windmill  may  be  used  to  advantage 
in  irrigating  small  areas  of  two  to  five  acres,  but  in  such 
cases  it  will  usually  be  necessary  to  provide  a  reservoir  of 
suitable  size  into  which  the  water  may  be  pumped  and 
stored. 


532 


Farm  Mechanics. 


For  wood  sawing  also  the  windmill  may  often  be  used 
to  advantage,  bj  getting  everything  in  readiness  to  do  the 
work  on  those  days  when  the  wind  shall  be  strong,  but  for 
this  kind  of  work  mills  as  large  as  12  to  16  feet  in  diameter 
are  required. 

668.  Wind  Pressure — The  pressure  which  the  wind  may 
exert    upon    a  surface    depends    primarily    upon  (1)  its 
weight  per  cubic  foot,  (2)  its  velocity,  and  (3)  the  angle 
at  which  it  strikes  the  surface.     The  weight  of  the  wind 
per  cubic  foot  is  greater  when  the  air  temperature  is  low 
and  when  the  barometric  pressure  is  high ;  this  being  true, 
the  capacity  of  a  windmill  in  a  given  place  varies  with  the 
season,  being  greatest  in  winter  and  least  in  summer,  for 
like  wind  velocities. 

As  the  weight  of  a  cubic  foot  of  air  decreases  with  alti- 
tude windmills  at  sea  level  can  do  more  work  than  those 
at  bights  of  1,000,  2,000  or  3,000  feet,  when  the  air  tem- 
peratures and  wind  velocities  are  equal. 

669.  Relation   of  Wind   Pressure   to   Wind  Velocity. — 
When  conditions  are  similar  wind  pressures  increase  as 
the  squares  of  the  wind  velocity.     Thus,  if  the  wind  pres- 
sure at  5  miles  per  hour  is  taken  as  1,  then  at  10,  15,  20, 
25,  30,  35  and  40  miles  per  hour  the  wind  pressure  will 
increase  in  the  ratio  of  the  squares  of  the  numbers  2,  3,  4, 
5,  6,  T,  8  ;  that  is  to  say,  a  10  mile  wind  may  exert  4  times 
the  pressure  that  a  5  mile  wind  does,  and  a  40  mile  wind 
a  pressure  64  times  as  great. 

Taking  the  air  at  a  pressure  of  2,116.5  Ibs.  per  sq.  ft. 
the  wind  pressures  at  different  velocities  and  temperatures 
will  be  as  stated  in  the  table  below : 

Table  giving  the  pressure  of  the  wind  per  sq.ft.  at  different 
velocities  and  temperatures  when  the  barometric  pressure 
remains  the  same.  (  Wolff.) 


Wind  velocity,  miles  per  hour.. 

5 

10 

15 

20 

25 

30 

35 

40 

Pressure  at  temperature  of  H0°  F 

.126 

.505 

1.135 

2.0l?< 

3.156 

4.548 

6.195 

8.099 

Pressure  at  temperature  of  60°  F 

.1187 

.475 

i.o  jy 

1.902 

2.973 

4.284 

5.836 

7.628 

Windmill. 


WO.  Ability  of  Wind  to  Do  Work.— The  work  which 
wind  can  do  depends  upon  the  amount  which  passes 
through  a  given  windmill  per  minute  and  the  pressure 
which  it  exerts,  But  as  the  pressure  varies  with  the  square 
of  the  velocity,  and  the  quantity  passing  the  mill  varies  di- 
rectly as  the  velocity,  the  theoretic  working  capacity  of  the 
wind  must  increase  as  the  cubes  of  the  wind  velocity. 


Thus  with  miles  per  hour  of  — 

5 

10 

15 

20 

25 

30 

35 

40 

Or,  taniiiK  5  =  to  1  they  are  as  . 

1 

2 

3 

4 

5 

6 

7 

8 

The  relative  horse-powers  are  as- 

1 

8 

27 

64 

125 

2lf 

34H 

512 

Theoretical  horse-power  is  

.025 

.2 

.675 

1.6 

3.125 

5.4 

8.575 

12.8 

Perry  regards  it  approximately  correct  to  state  that  a 
12  ft.  windmill  in  a  5  mile  wind  may  develop  ^  of  a 
horse-power  and  the  figures  in  the  last  line  in  the  table 
above  are  his. 


671.  Relation  of  Diameter  of  Wheel  to  Its  Efficiency. — In 
increasing  the  horse-power  of  an  engine  it  is  not  usually 
necessary  to  increase  its  weight  and  strength  much  more 
than  in  proportion  to  the  increase  of  power  which  is  to  be 
developed,  but  in  the  case  of  two  wind  wheels,  having  the 
same  type  of  construction,  the  one  which  is  to  develop 
double  the  horse-power  must  have  a  strength  of  resistance 
practically  8  times  as  great  in  order  to  withstand  the  high- 
est wind  pressures  to  which  it  is  liable  to  be  subjected.  This 
is  so  because  doubling  the  diameter  of  the  wheel  not  only 
makes  the  surface  of  wind  pressure  four-fold,  but  at  the 
same  time  carries  the  center  of  pressure  farther  from  the 
axis  of  the  wheel,  causing  it  to  act  upon  a  longer  lever 
arm.  But  to  increase  the  strength  of  resistance  of  the 
wheel  8-fold  makes  it  necessary  to  build  it  much  heavier 
and  this  detracts  from  its  relative  efficiency. 

Besides  this,  with  wheels  of  large  diameter  there  are 
much  greater  differences  in  the  wind  pressure  on  the  dif- 
ferent parts  of  the  wind  sails  because  the  actual  velocity 


534:  Farm  Mechanics. 

of  the  sails  increases  with  the  distance  of  their  points  from 
the  center  of  the  wheel.  But  the  angular  velocity  must  be 
the  same  in  all  parts  of  the  sail,  and  this  causes  the  wind 
sail  to  be  forced  around  away  from  the  wind  passing 
through  the  wheel  with  very  different  velocities,  and  this 
difference  reduces  the  relative  efficiency  so  that  large  wind- 
mills of  like  pattern  do  not  increase  the  available  horse- 
power as  much  as  the  size  is  increased. 

672.  Unsteadiness  of  Wind  Velocity. — It  should  be  under- 
stood that  the  wind  rarely  blows  with  anything  like  uni- 
form velocity  for  even  a  single  minute,  and  an  anemometer 
which  gives  the  total  number  of  miles  of  wind  in  an  hour 
furnishes  no  sufficiently  reliable  data  from  which  to  cal- 
culate the  work  which  the  windmill  should  be  expected  to 
do.  It  very  often  happens  that  a  wind  which  is  registered 
as  10  miles  per  hour  may  have  been  blowing  during  a  con- 
siderable portion  of  the  time  at  the  rate  of  20  miles  per 
hour  and  these  high  velocities  are  very  much  more  effective 
than  the  mean  10-mile  wind,  and  this  would  cause  the 
wheel  to  show  a  relatively  high  efficiency  in  such  a  case. 

673.  Hight  of  Towers. — The  wind  velocity  near  the 
earth's  surface  is  not  only  less  than  at  higher  elevations 
at  the  same  time,  but  near  the  ground  it  is  very  much  less 
uniform,  so  that  for  both  of  these  reasons  mills  should  be 
placed  upon  as  high  towers  as  practicable  when  the  great- 
est efficiency  is  desired.  If  there  are  obstructions  to  the 
wind  movement  even  within  1,000  feet  of  the  windmill 
the  tower  should  carry  it  several  feet  higher  than  these. 
Observations  indicate  that,  taking  the  velocity  of  the  wind 
at  a  hight  of  50  feet  as  1,  at  25  feet  its  velocity  would  be 
nearly  .8 ;  at  75  feet  it  would  be  1.2  and  at  100  feet  it 
would  be  nearly  1.4.  These  are  deduced  from  Steven- 
son's formula,*  which  is 

H+72 
V  =  v~122~ 

•  Journal  of  the  Scottish  Meteorological  Society,  1881, 


Windmill.  535 

where  V  is  the  velocity  at  the  hight  of  the  tower,  v  the  ve- 
locity at  50  feet,  and  H  the  hight  of  the  windmill. 

Taking  the  efficiency  of  the  wind  as  increasing  with  the 
cube  of  the  velocity,  the  relative  efficiency  of  the  same  mill 
at  the  four  hights  would  be  at  25  feet  .51,  at  50  feet  1,  at 
75  feet  1.73  and  at  100  feet  2.74,  from  which  it  appears 
that  a  mill  placed  on  a  100-foot  tower  may  have  more  than 
5  times  the  efficiency  of  one  placed  at  25  feet,  and  a  mill 
on  a  75  foot  tower  is  likely  to  do  three-fourths  more  work 
than  one  on  a  50-foot  tower. 

674.  Observed  Amount  of  Work  Done  by  a  Windmill  in 
Pumping  Water. — We  have  measured  the  amount  of  water 
which  was  pumped  during  one  entire  year  by  the  16-foot 
geared  windmill  represented  on  the  cover  of  this  book.* 
This  mill  was  provided  with  three  pumps  arranged  so  as 
to  lift  water  12.85  feet  whenever  there  was  wind  enough 
to  enable  it  to  do  any  work.  When  the  wind  was  lightest 
it  was  given  the  pump  of  smallest  capacity,  when  stronger 
the  one  of  next  size,  when  still  stronger  both  pumps  to- 
gether, the  third  pump  being  used  only  in  the  very  high- 
est winds. 

The  water  was  pumped  into  a  large  tank  holding  141.2 
cu.  ft.,  so  arranged  that  when  full  it  emptied  itself  auto- 
matically in  f  of  a  second,  and  at  the  same  time  recorded 
the  time  of  emptying.  In  connection  with  this  an  auto- 
matic U.  S.  Weather  Bureau  anemometer  made  a  continu- 
ous record  of  the  miles  of  wind  passing  through  the  mill 
each  hour  of  the  day  for  a  whole  year  and  the  amount  of 
water  pumped  during  the  same  intervals. 

The  amount  of  work  done  by  this  windmill  during  10- 
day  periods  for  the  whole  year  is  computed  in  acre-inches 
of  water  lifted  to  a  hight  of  10  feet  and  expressed  in  the 
table  below: 

•Bulletin  68,  Wisconsin  Agricultural  Experiment  Station. 


536 


Farm  Mechanics. 


Table  showing  computed  amount  of  water  lifted  10  feet  high 
during  consecutive  10-day  periods  for  one  full  year,  ex- 
pressed in  acre-inches. 


Date. 

Water 
pumped. 

Date. 

Water 
pumped. 

Date. 

Water 
pumped. 

Feb.  28-Mch.  10 

Acre-  in. 
33.f4 

July  8-18... 

A  ere-  in. 
21.53 

Nov.  15-25  

Acre-in. 
53.77 

Mch.  10-20  

3<j.62 

July  JS-23.... 

29.73 

Nov.  25-Dec.  5 

47.46 

Mch.  20-30  

52.77 

July  28-Aug.  7 

9.87 

Dec.  5-15  

39  52 

Mch.  30-Apr.9.. 
Apr.  9-19  
Apr.  19-29  

47.01 
54.11 
63.05 

Au<r-  7-17  
Aug.  17-27.... 
Aug.  27-Sept.  6 

36  26 
20.20 
21.27 

Dec.  15-25.... 
Dec.  25-Jan.  4 
Jan.  4-14  

31.18 
51  22 
33  92 

Apr.  29-May  9.. 
May  9-19  

59.97 
28.69 

Sept.  6-16  .... 
Sept.  16-26  .  .  . 

18.00 
40.42 

Jan.  14-?».... 
Jan.  24-Feb.  3 

29.16 
59  36 

May  19-29.     .  .  . 

51  33 

Sept.  26-Oct.  6 

23.79 

Feb.  3-13  

33  45 

May  29-June  8.. 

40.54 

Oct.  6-16  

55  07 

Feb.  11  23.... 

75  73 

June  8-18 

27  59 

Oct.  16-26.  .     . 

18  45 

Feb.  23-28..  . 

16  20 

June  18-28  

13  82 

Oct.  26-Nov.  5.. 

36.71 

June  2S-July  8.. 

26.68 

Nov.  5-15  

49.  49 

It  will  be  seen  from  this  table  that  the  smallest  amount 
of  water  lifted  ten  feet  high,  in  10  days,  was  enough  to 
cover  9.87  acres  one  inch  deep  and  this  occurred  from  July 
28  to  August  7,  at  the  time  when  water  for  irrigation  is 
most  needed.  The  largest  amount  pumped  occurred  dur- 
ing the  10  days,  from  Feb  13  to  23,  and  was  enough  to 
cover  75.73  acres  one  inch  deep. 

675.  Observed  Amount  of  Work  Done  by  a  Windmill  in 
Grinding  Feed. — Another  set  of  trials,  aiming  to  measure 
the  amount  of  feed  which  may  be  ground  with  a  12-foot 
geared  windmill,  was  made  at  the  Wisconsin  Experiment 
Station,*  and  using  the  observed  amounts  of  corn  ground 
under  a  wide  range  of  wind  velocities  and  the  observed 
hourly  wind  velocities,  as  recorded  for  the  pumping  exper- 
iment, the  amount  of  feed  which  could  have  been  ground, 
had  it  been  fed  automatically  and  kept  running  continu- 
ously, has  been  computed  and  given  in  the  table  which  fol- 
lows: 

*  Bulletin  82,  Wisconsin  Agricultural  Experiment  Station. 


Windmill. 


137 


Table  showing  the  amount  of  corn  which  could  have  been 
ground  by  the  12-foot  acrmotor  windmill  during  the  year, 
from  March  6,  1897,  to  March  6,  1898,  with  all  winds  from  9 
miles  to  30  miles  per  hour. 


Wind, 

No.  of 

Amount 

Total 

Wind, 

No.  of 

Amount 

Total 

iiiiJr-;  por 

Lours  of 

ground 

meal 

miles  per 

hours   of 

ground 

meal 

hour. 

wind. 

per  hour. 

ground. 

hour. 

wind. 

per  hour. 

ground. 

Jbs. 

Ibs. 

Ibs. 

lb*. 

9 

480 

2U.61 

9,»91 

20 

195 

515.10 

10:  1,400 

10 

559 

38.31 

21,410 

21 

144 

592.8 

f-5,360 

11 

495 

61.46 

30,430 

22 

114 

675.9 

77,050 

12 

425 

90.07 

33,280 

23 

112 

764.4 

81.610 

13 

406 

124.10 

50,4uO 

24 

92 

858.4 

78,970 

?4 

401 

164.00 

65,  770 

25 

71 

957.8 

68,010 

15 

341 

208.60 

71,  ISO 

26 

70 

1,063.0 

7J.390 

16 

328 

259.00 

84,950 

27 

57 

1,173.0 

66,  870 

17 

264 

314.90 

83,  120 

28 

44 

1.2S9.0 

56,710 

18 

238 

376.10 

83,880 

29 

40 

1.410.0 

5ri,  40J 

19 

M93 

44;!.  90 

85,480 

30 

33 

1,537.0 

50,710 

The  total  footing  of  this  table  shows  that  the  mill  might 
have  ground  an  average  of  about  75  bushels  of  corn  per 
day  for  the  entire  year,  but  this  figure  would  represent  the 
maximum  amount  of  work  possible.  The  minimum  could 
hardly  have  been  less  than  &  of  this  amount. 


CHAPTER  XXIIL 
FARM  MACHINERY. 

FRICTION. 

It  has  never  been  practicable  to  devise  a  machine  which 
could  transmit  the  energy  imparted  to  it  without  sustain- 
ing a  certain  amount  of  loss  through  friction  and  in  some 
forms  of  machines  the  loss  of  power  through  friction  is 
necessarily  very  great  under  the  best  management.  In 
other  cases  ignorance  of  the  laws  of  friction  or  carelessness 
leads  to  much  larger  losses  than  are  necessary. 

On  the  other  hand  friction  may  be  a  very  essential  con- 
dition to  the  accomplishing  of  important  results.  How  es- 
sential it  is  in  walking  we  appreciate  when  we  attempt  to 
move  over  very  smooth  ice  and  it  is  the  friction  of  the 
drivers  of  the  locomotive  upon  the  rails  which  enables  it  to 
haul  the  enormous  loads  it  does.  In  transmitting  power 
by  means  of  belts  it  is  friction  which  enables  it  to  be  done. 
The  service  of  nails  and  screws  in  holding  parts  together 
depends  upon  the  amount  of  friction  developed  in  forcing 
them  home. 

676.  Friction  Between  Solids. — When  one  surface  rests 
upon  another  there  is  a  tendency  for  the  inequalities  of 
one  to  fit  into  those  of  the  other,  producing  an  interlocking 
not  very  unlike,  except  in  degree,  what  would  be.  produced 
by  putting  the  cutting  edges  of  two  saws  together.  When 
such  an  interlocking  has  occurred  it  is  only  possible  to 
move  one  surface  over  the  other  by  either  separating  the 
two  surfaces  slightly  or  else  by  tearing  off  the  interlocking 
portions,  and  it  is  the  separating  of  the  two  bodies  or  1:he 
abraiding  of  these  inequalities  which  causes  the  chief  part 


Friction.  539 

of  friction  between  solids.  Because  of  the  molecular 
structure  of  bodies,  no  matter  how  smoothly  the  two  fric- 
tion surfaces  are  polished,  there  must  still  remain  eleva- 
tions and  depressions  which  permit  interlocking.  There 
is  also  a  slight  adhesion  between  the  two  surfaces  which 
adds  a  small  amount  to  the  friction ;  from  this  it  follows 
that  no  two  surfaces  can  slide  over  one  another  without 
developing  the  resistance  known  as  friction. 

677.  Friction  of  Rest  or  Static  Friction  Between  Solids. — 
Whenever  one  body  is  brought  to  rest  upon  another  over 
which  it  is  sliding,  the  jarring  which  takes  place  at  the 
time  causes  the  upper  body  to  fall  from  the  higher  inequal- 
ities into  the  depressions  of  the  lower  one,  thus  developing 
the  maximum  interlocking  due  to  this  cause.     Then  again, 
after  long  standing,  if  there  has  been  considerable  pres- 
sure, the  plasticity  of  the  substances  will  cause  them  to  in- 
terlock still  more  completely,  and  so  it  happens  that  the 
amount  of  force  required  to  overcome  friction  between 
two  solid  surfaces  at  rest  is  always  greater  than  the  force 
required  to  keep  the  body  moving  after  the  static  friction 
has  been  overcome,  and  Thurston  states  that  it  is  commonly 
40  per  cent,  greater.     The  case  is  not  profoundly  unlike 
the  difficulty  in  starting  a  loaded  wagon  after  it  has  stood 
over  night  and  formed  a  depression  under  each  wheel. 

678.  Friction  of  Motion  Between  Solids. — After  one  solid 
surface  is  once  started  sliding  over  another  time  enough 
does  not  intervene  in  passing  from  inequality  to  inequality 
to  permit  maximum  interlocking  to  take  place,  and  the  re- 
sult is  the  smaller  amount  of  friction  of  motion,  compared 
with  that  of  rest,  stated  in  (677). 

The  amount  of  sliding  friction  can  be  simply  illustrated 
by  using  inclined  planes  with  different  kinds  of  surfaces, 
by  first  placing  the  plane  and  then  putting  upon  this  the 
object  whose  friction  is  to  be  determined.  By  gradually 
elevating  the  plane  and  jarring  it  a  little  an  inclination 
will  be  reached  at  which  the  body  will  slide  down  the  sur- 


540  Farm  Mechanics. 

face  with  a  uniform  velocity.  Suppose  the  hight  to  which 
the  end  of  the  plane  has  been  raised  is  just  iV  of  its  base, 
then  the  friction  of  motion  is  10  per  cent., — that  is,  it  will 
require  a  force  equal  to  tV  of  the  weight  of  the  load  to 
maintain  motion. 

It  has  been  found  that  usually  the  sliding  friction  be- 
tween non-lubricated  surfaces  increases  directly  as  the 
weight  but  is  independent  of  the  area  of  surface,  provided 
the  weight  is  not  great  enough  to  cut  or  tear  them.  Gen. 
Morin  found,  in  his  experiments,  that  wood  without  lubri- 
cant showed  a  friction  of  25  to  50  per  cent.,  but  when  soap 
was  used  between  the  surfaces  the  friction  was  reduced  to 
from  4  to  20  per  cent.  In  the  case  of  metal  on  wood,  with- 
out lubricant,  he  found  it  to  be  from  50  to  60  per  cent. 
With  the  smoothest  and  best  lubricated  surfaces  he  found 
it  as  small  as  3  to  3.6  per  cent. 

679.  Rolling  Friction. — When  one   solid   surface   rolls 
over  another,  no  matter  how  smooth  they  may  be,  there  is 
always  friction,  but  the  amount  is  much  less  than  that  of 
sliding,  and  the  fundamental  reason  is  the  same  as  that 
which  permits  a  load  to  be  carried  over  bare  ground  on 
wheels  with  less  friction  than  when  carried  upon  a  sled. 
The  roller  bearings  in  common  use  on  the  grindstone  illus- 
trate the  smaller  friction  due  to  the  use  of  rollers,  but  we 
get  the  most  perfect  example  of  reduced  friction  in  the 
ball  bearings  of  bicycles. 

680.  Friction  Between  Liquids. — The  laws  governing  the 
friction  of  liquids  are  very  different  from  those  of  solids. 
In  the  first  place  it  increases  with  the  square  of  the  veloc- 
ity, instead  of  directly  as  the  velocity  in  the  case  of  solids, 
and  it  decreases  with  increase  of  temperature  of  the  liquid, 
often  to  a  very  important  extent. 

The  liquids  used  as  lubricants  have  generally  compara- 
tively high  viscosity,  as  fluid  friction  is  technically  called, 
and  they  vary  between  wide  limits  among  themselves,  es- 
pecially when  they  experience  wide  changes  of  tempera- 


Friction.  541 

tnrc.  The  oils  and  fats  suitable  for  lubricants  belong  to 
both  the  animal  and  vegetable  and  the  mineral  non-drying 
types.  Any  oil  or  fat  which  becomes  permanently  gummy 
and  stiff  after  the  exposure  of  service  makes  a  very  unsatis- 
factory machine  lubricant,  and  although  such  oils  can  be 
found  upon  the  market,  selling  at  a  lower  price  than  the 
best  lubricants,  it  is  seldom  economy  to  use  them  because 
they  soon  gum  up  the  bearings,  greatly  increase  the  fric- 
tion and  increase  the  labor  necessary  to  put  the  machine 
into  condition  again.  In  special  cases  finely  divided 
solids,  like  graphite  and  soapstone,  are  used  as  lubricants. 

681.  The    Action    of    Lubricants. — When     liquids     are 
brought  into  contact  with  solid  surfaces  to  which  they  ad- 
here, as  in  the  case  of  water  flowing  through  pipes,  there 
is  a  thin  la'yer  held  to  the  walls  of  the  pipe  so  rigidly  that 
it  hardly  takes  part  in  the  flow,  so  that  instead  of  having 
the  friction  of  a  liquid  upon  a  solid,  the  slipping  takes 
place  between  layers  of  the  liquid  itself.     So,  too,  when  an 
oil  is  poured  into  the  bearings  of  a  machine  there  come  to 
be  two  comparatively  stationary  layers  against  the  two 
metal  surfaces  and  the  sliding  or  friction  takes  place  be- 
tween layers  of  oil  rather  than  between  layers  of  metal, 
and  it  is  because  the  friction  of  lubricants  upon  themselves 
is  so  much  less  than  that  between  solids  that  they  are  so 
serviceable. 

The  lubricant  may  act  in  two  different  ways  in  lessening 
the  friction:  (1)  by  causing  the  chief  part  of  the  resist- 
ance to  be  that  due  to  the  slipping  of  oil  over  oil,  which  is 
usually  less  than  the  friction  between  solids,  and  (2)  by 
the  lubricant  acting  to  fill  up  the  smaller  inequalities  of 
the  two  friction  surfaces  and  in  this  way  preventing  so 
much  interlocking. 

682.  Adaptation    of   Lubricant    to    Place    of   Service. — 
Where  the  speed  of  the  sliding  surfaces  is  relatively  high, 
and  especially  if  the  pressure  between  the  bearings  is  not 
heavy,  one  of  the  thin  oils  will  render  the  best  service, 


542  Farm  Mechanics. 

securing  the  least  friction.  On  the  other  hand,  if  the  bear- 
ings are  carrying  heavy  pressure  at  a  slow  rate  of  sliding, 
as  in  the  case  of  the  axles  of  wagons,  then  the  heavy  thick 
oil  or  grease  will  last  longer,  maintain  less  wear  of  the 
bearings  and  ensure  a  smaller  friction.  But  in  any  case 
the  rate  of  revolution  of  parts  and  the  amount  of  friction 
must  be  so  related  that  sufficient  heat  is  not  developed  to 
burn  the  oil.  Further  than  this  it  may  sometimes  happen 
that  the  oil  does  not  feed  rapidly  or  completely  enough  to 
all  parts  of  the  bearing  to  ensure  perfect  lubrication  and 
constant  watchfulness  is  required  on  the  part  of  every 
operator  of  a  machine  to  keep  things  in  proper  condition. 

683.  Scrupulous  Cleanliness  of  Bearings — Next  in  impor- 
tance to  good  lubrication  of  all  slipping  portions  of  a  ma- 
chine stands  the  maintenance  of  scrupulously  clean  bear- 
ings, where  the  friction  surfaces  are  free  from  both  grit 
or  any  gummy  substance.     Where  sand  or  grit  of  any  sort 
has  found  its  way  to  the  bearings  of  machinery  its  grains 
cut  through  the  film  of  oil  on  both  friction  surfaces  and 
tend  to  lock  the  two  together  in  the  same  manner  that  sand- 
ing the  rail  under  the  driver  of  a  locomotive  does  and  thus 
prevent  slipping. 

Because  of  this  tendency  of  dirt  to  get  into  bearings, 
even  under  the  best  management,  it  is  necessary  to  occa- 
sionally overhaul  the  bearings  of  important  machines  and 
carefully  clean  them,  and  very  special  attention  should  be 
given  to  all  those  parts  where  the  speed  is  high,  because 
not  only  is  here  where  power  is  absorbed  most  rapidly  by 
needless  friction  but  the  wearing  and  injury  to  the  ma- 
chine is  most  rapid. 

684.  Hot  Boxes. — The  heating  of  boxes  in  machinery 
may  result  from  one  or  more  of  several  causes:  (1)  insuf- 
ficient lubrication/  (2)  dirt  in  the  journal,  (3)  the  box 
may  be  screwed  down  too  tight,  (4)  the  belt  may  be  too 
tight,  producing  unnecessary  friction,   (5)  the  box  may 


Belting.  543 

have  gotten  out  of  line  with  the  shaft,  (6)  the  collar  or 
pulley  may  bear  too  hard  against  the  end  of  the  box. 

BELTING. 

The  use  of  belting,  ropes  and  cables,  in  transmitting 
power  from  a  motor  to  the  machine  being  driven,  is  a  prac- 
tical utilization  of  friction. 

685.  Action   of   Belting. — When    machinery    is    being 
driven  by  a  belt  its  two  sides  are  not  under  equal  tension 
and  the  efficiency  of  the  belt  depends  upon  the  difference 
in  tension  between  the  two  sides  and  the  rate  at  which  the 
belt  is  traveling.     Suppose  the  effective  tension  of  the  belt 
is  66  Ibs.  and  that  the  belt  is  traveling  with  a  velocity  of 
1,000  feet  per  minute,  then  the  energy  it  is  transmitting, 
or  its  activity,  is  equal  to 

66  X  1000  =  66,000  fcot  pounds  per  minute. 
or  66,000  _ 

33,000- 

It  is  clear  from  this  that  the  more  rapidly  the  belt  is 
driven  the  larger  is  the  horse-power  transmitted  when  the 
effective  tension  of  the  belt  is  the  same. 

686.  Efficiency  of  Belting. — The  highest  efficiency  is  at- 
tained from  belting  when  there  is  least  stretching  and  least 
slipping  of  the  belt  and  when  there  is  the  least  unnecessary 
pressure  developed  by  it  on  the  shafts  of  the  driving  pul- 
leys. 

Good  leather  belts  usually  give  a  higher  efficiency  than 
rubber  or  other  types  and  when  they  are  used  where  they 
can  always  be  kept  dry  are  most  satisfactory.  To  get  the 
highest  service  from  a  leather  belt  it  should  be  run  with 
the  hair  side  next  to  the  pulley  and  over  a  pulley  faced 
with  leather  with  the  hair  side  out.  Under  these  condi- 
tions there  is  the  least  slipping  of  the  belt  and  the  strain 
on  the  belt  in  bending  around  the  pulley  is  least,  so  that  it 
wears  more  slowly  when  being  bent  and  straightened. 


544  Tarm  Mechanics. 

687.  Size  of  Belt  for  Transmission  of  Given  Horse-Power. 
— In  order  not  to  over-strain  a  good  two-ply  leather  belt 
it  ought  not  to  be  subjected  to  an  effective  tension  of  more 
than  40  pounds  per  inch  of  width.     On  this  basis  the  width 
of  belt  for  a  given  number  of  horse-power  will  depend 
upon  the  speed  of  the  belt.     Suppose  the  driving  pulley  of 
an  engine  is  9  inches  and  that  it  makes  350  revolutions 
per  minute,  developing  3  horse-power.     What  width  of  belt 
would  be  required  ?     This  may  be  calculated  from  the  fol- 
lowing equation. 

3  X  33  000 
3.1416  X.  75X350X40  =  3™1  inchea'  width  of  belt 

In  this  case  3  is  the  number  of  H.  P.,  33,000  is  the 
number  of  foot-pounds  in  one  H.  P.,  3.1416  x  .75  x  350 
gives  the  velocity  of  the  belt  in  feet  per  minute  and  40 
is  the  effective  tension  to  which  the  belt  may  be  safely 
subjected.  From  this  solution  a  general  equation  for  cal- 
culating the  width  of  belt  for  any  H.  P.  may  be  stated  as 
follows, 

nr.-m.    ,uu.      No.  H.  P.  X  33,  OOP 
Width  of  belt  =  gpxNo.rev.x40 

D  =  circumference  of  driving  pulley  in  feet. 

No.  rev.  =  number  of  revolutions  of  driving  pulley  per  minute. 

Some  belt  manufacturers  allow  a  strain  of  60  pounds 
per  inch  of  width  for  a  two-ply  leather  belt  as  safe  but 
it  is  in  the  direction  of  economy  to  have  the  belt  stronger 
than  is  really  necessary,  as  it  will  wear  enough  longer 
to  pay. 

688.  Condition  of  Belt. — It  is  very  important  to  keep  the 
belt  in  a  good,  soft,  pliable  condition,  as  a  flexible  belt 
will  not  only  transmit  power  with  less  loss  but  it  will  wear 
much  longer.     If  for  any  reason  belts  have  become  hard 
and  stiff,  they  should  be  softened  with  neatsfoot  oil.     New 


Belting.  545 

belts  always  stretch  more  at  first  than  after  they  have  been 
used. 

689.  Pulley  and  Shaft — In  order  that  a  belt  may  run 
well  on  the  pulley  it  is  essential  that  the  shafts  of  the  two 
pulleys  connected  by  the  belt  shall  be  rigidly  parallel  with 
each  other  and  that  the  pulleys  shall  turn  true  on  the  shafts. 
When  the  pulleys  are  properly  placed  the  belt  will  run  to 
the  center  of  the  pulley  and  stay  there. 

Belts  tend  to  run  to  the  largest  part  of  the  pulley  and 
for  this  reason  pulleys  are  commonly  made  a  little  crown- 
ing in  the  center  so  as  to  cause  the  belt  to  run  to  the  center. 
But  where  tight  and  loose  pulleys  run  side  by  side,  so  as 
to  throw  off  the  belt  without  stopping  the  power,  then 
the  faces  of  the  pulleys  are  flat. 

In  running  a  belt  onto  a  pulley,  especially  when  it  is 
wide,  heavy  and  tight,  care  needs  to  be  taken  not  to  over- 
strain it  as  there  is  danger  of  stretching  the  edge  so  that 
it  will  never  run  true  afterwards,  or  even  of  cutting  or 
tearing  it,  especially  if  the  edge  of  the  pulley  happens 
to  be  sharp. 

690.  Lacing  a  Belt. — In  lacing  a  belt  care  should  be 
taken  to  make  the  lacing  plenty  strong  enough,  but  to 
make  it  unnecessarily  so  is  worse  than  to  have  it  a  little 
light,  especially  if  it  has  been  done  in  a  bungling  manner 
so  as  to  form  an  enlarged  place  in  the  belt  which  brings 
undue  strain  when  the  lacing  is  passing  the  pulleys.     The 
lacing  should  be  so  nicely  done  that  this  portion  of  the 
belt  passes  the  pulley  without  a  jar  or  extra  strain.     To 
secure  this  the  ends  of  the  belt  should  be  cut  true  and 
square  by  using  a  try-square.     Holes  should  be  punched 
just  large  enough  to  allow  the  lacing  to  fill  them  well 
without  danger  of  tearing  them  out  by  wedging.     Space 
the  holes  equally,  leaving  the  outside  ones  just  far  enough 
from  the  edge  to  be  safe  against  tearing  out,  and  they 
should  be  not  more  than  |  to  £  an  inch  from  the  ends. 

Sew  with  the  smooth  side  of  the  lacing  out,  beginning 


546  "Farm  Mechanics. 

at  the  center  of  the  belt,  and  never  cross  it  or  have  more 
than  two  thicknesses  of  lacing  on  the  side  next  to  the 
pulley.  Fasten  the  lacing  by  running  the  ends  through 
small  holes  punched  in  line  with  the  lace  holes  where  they 
will  be  in  the  right  place  to  serve  as  lacing  holes  when 
the  belt  needs  to  be  shortened. 

691.  Calculating  the  Length  of  Belts. — To  ascertain  the 
exact  length  of  a  belt  to  connect  two  pulleys  measure  the 
exact  distance  between  the  centers  of  the  two  pulley  shafts. 
Then  add  the  circumferences  of  the  two  pulleys  together, 
dividing  the  sum  by  two;,  add  this  sum  to  twice  the  dis- 
tance between  the  centers  of  the  two  shafts  and  the  total 
is  the  length  of  belt  required. 


FAEM  PUMPS. 

There  are  several  forms  of  devices  used  in  lifting  water 
on  the  farm,  chiefly  for  the  use  of  the  stock  and  as  a  water 
supply  for  the  house ;  these  are  known  as  suction  and  force 
pumps  and  hydraulic  rams. 

692.  Suction  Pump. — The  common  suction  pump  consists 
of  a  cylinder  and  piston  connected  below  with  a  suction 
pipe,  and  above  with  a  discharge  pipe.  At  the  upper  end 
of  the  suction  pipe,  usually  in  the  lower  end  of  the  cylin- 
der, below  the  piston,  there  is  the  suction  valve  which  opens 
upward  by  the  force  of  the  water  but  closes  with  the  down 
stroke  of  the  piston,  preventing  the  return  of  water  to  the 
well.  In  the  piston  is  a  second  valve,  also  opening  upward 
which  permits  the  piston  to  be  forced  downward  through 
the  water  in  the  cylinder,  held  there  by  the  suction  valve, 
but  which  closes  the  moment  the  piston  begins  to  rise  and 
thus  lifts  whatever  water  is  above  the  valve,  at  the  same 
time  tending  to  produce  a  vacuum  below  the  piston  into 
which  the  pressure  of  the  air  on  the  water  of  the  well 
lifts  the  water  through  the  suction  pipe  -and  past  the  suc- 
tion valve  already  described. 


Suction  Pump.  5 17 

The  piston  is  usually  worked  by  a  simple  lever  in  the 
form  of  the  pump  handle  and  the  water  is  discharged 
through  the  spout  in  the  pump-head  near  the  level  of  the 
ground. 

693.  Size  of  Piston — The  size  of  piston  which  should  be 
used  in  a  well  depends  upon  the  hight  to  which  the  water 
must  be  lifted  and  the  power  which  is  available  to  work 
the  pump.  In  working  a  common  pump  a  man  can  com- 
fortably exert,  a  pressure  of  only  15  to  20  pounds  upon  the 
pump  handle  and,  as  the  power  arm  of  this  lever  is  only  5 
to  7  times  that  of  the  weight  arm,  the  pressure  exerted 
by  the  water  to  be  lifted  at  one  stroke  cannot  much  exceed 
75  to  100  pounds.  Water  at  ordinary  well  temperature 
exerts  a  pressure  of  .43  pounds  per  square  inch  for  each 
foot  of  depth.  This  being  true,  whenever  the  piston  is 
called  upon  to  lift  water  through  a  hight  of  40  feet  the 
pressure  on  the  piston  would  be  at  the  rate  of 

40  X  -43  =  17.2  Ibs.  per  sq.  in. 

A  2-inch  piston  has  an  area  of  3.14  square  inches,  a  2.5 
inch  piston  4.9  square  inches,  a  3-inch  piston  7.07  and 
a  3.5-inch  piston  9.62  square  inches,  so  that  in  lifting 
water  through  40  feet  with  each  one  of  these  pistons  the 
force  required  to  be  applied  to  the  piston  rod  would  have 
to  be 

Forthe2     inch  piston 54.01  Ibs. 

For  the  2.5  inch  piston 81  28  Ibs. 

For  the  3     inch  piston 121.60  Ibs. 

For  the  3.5  inch  piston 165.46  Ibs. 

It  will  be  clear  from  these  figures  that  for  ordinary  hand 
pumping  a  2  to  2.5-inch  piston  is  as  large  as  can  be  com- 
fortably worked  in  a  Avell  where  the  lift  must  equal  40 
feet.  If  the  well  has  such  a  depth  that  the  water  must  be 
lifted  100  feet  the  2-inch  piston  would  sustain  a  pressure 
of  135  pounds  and  hence  would  be  larger  than  could  be 
comfortably  worked  in  such  a  well, 


548  Farm  Mechanics. 

694.  Kate  of  Pumping — The  rate  of  discharge  from  a 
common  single  acting  suction  pump  is  determined  by  the 
area  of  effective  cross-section  of  the  cylinder,  the  length 
of  the  stroke  and    the   number   of   strokes    per    minute. 
Taking  a  2.5-inch  cylinder,  which  would  have  an  effect- 
ive cross-section  of  about  4.7  square  inches  and  supposing 
it  to  make  a  5-inch  stroke  at  the  rate  of  30  per  minute, 
the  amount  of  water  pumped  per  hour  would  be 

4.7X5X30X60 

— nor —        —  —  183.1  gallons. 

or  enough  for  about  21  cows  allowing  72  pounds  per  head. 

695.  Relation  of  Size  of  Suction  and  Discharge  Pipe  and 
Piston  to  Power  Required  to   Work   the    Pump. — When   a 
large  piston  is  worked  on  a  small  suction  and  discharge 
pipe  it  is  necessary  for  the  water  to  travel  much  faster 
through  these  than  when  they  have  an  effective  diameter 
equal  to  that  of  the  piston ;  but  to  increase  the  velocity  of 
flow  through  a  pipe  requires  an  increase  of  pressure  so  that 
more  power  is  required  to  pump  the  same  quantity  of 
water  through  a  1-inch  pipe,  using  a  3-inch  cylinder,  than 
to  pump  the  same  amount  in  the  same  time  through  a 
3-inch  pipe.     In  the  apparatus  represented  in  Fig.  259, 
when  the  pump  with  the  3-inch  cylinder  C  is  worked,  dis- 
charging water  through  the  3-inch  discharge  pipe  3,  lifting 
the  water  to  a  hight  of  about  18  feet  and  working  the 
pump  at  the  ordinary  rate,  the  pressure  gage  E  shows 
that  the  pumping  is  developing  a  pressure  of  about  9 
pounds  to  the  square  inch.     If  now  the  pump  is  kept  work- 
ing at  the  same  rate  and  the  gate  valve  in  3  closed,  while 
that  in  the  2-inch  pipe  is  opened,  the  pressure  is  seen  to 
rise  to  nearly  11  pounds  per  square  inch.     Then  on  open- 
ing the  gate  valve  in  the  1-inch  pipe  and  closing  that  in  the 
2-inch  the  pressure  rises  to  between  13  and  14  pounds,  but 
when  closing  the  1-inch  gate  and  opening  that  in  the   I  - 
inch  pipe  the  gage  registers  a  pressure  of  between  18  and 
19  pounds  per  square  inch  of  the  piston,  when  the  same 


Suction  Pump. 


549 


FIG.  259.— Apparatus  for  demonstrating  the  resistance  of  pipes  to  flow  of  water 
•     in  pumping. 


35 


550  Farm  Mechanics. 

amount  of  water  is  being  discharged  per  minute  as  when 
the  pump  was  being  worked  on  the  3-inch  discharge  pipe. 
From  these  observations  it  is  clear  that  the  size  of  the 
suction  and  discharge  pipe,  compared  with  the  piston, 
may  make  a  very  material  difference  in  the  amount  of 
power  necessary  to  work  the  pump  at  a  given  rate.  Tho 
area  of  the  3-inch  piston  contains  the  area  of  the  I  -inch 
pipe  nearly  16  times  and  this  means  that  when  the  piston 
is  driving  the  water  through  the  *  inch  pipe  its  velocity 
must  be  16  times  that  of  the  piston,  while  when  forcing  it 
through  the  3-inch  pipe  the  water  travels  at  only  the  same 
rate  and  therefore  requires  less  power. 

696.  Influence  of  Elbows  on  the  Power  Required  to  Work 
a  Pump. — In  the  apparatus  of  Fig.  259  there  is  repre- 
sented, leading  out  of  and  back  into  the  |-inch  pipe,  a  side 
tube,  so  that  when  the  f  inch  gate  valve  is  closed  and  the 
pump  worked  the  water  is  forced  to  travel  through  four 
right  angles  instead  of  taking  the  straight  course  possible 
when  the  gate  is  open.    Under  these  conditions  the  gage  E 
shows  an  increase  of  pressure  amounting  to    f  of  a  pound 
per  square  inch  for  each  right  angle,  or  a  total  increase 
of  three  pounds  per  square  inch  on  the  piston  and,  as  the 
piston  has  an  area  of  over  seven  square  inches,  the  extra 
power  which  had  to  be  applied  to  the  piston  rod,  in  order 
to  pump  around  the  four  elbows,  exceeded  28  pounds. 

697.  Double-Acting    Suction    Pumps. — In   the    ordinary 
suction  pump,  practically  all  of  the  work  has  to  be  done 
with  the  up  stroke  of  the  piston  and  this  requires  a  heavier 
pressure  than  would  be  necessary  if  the  work  could  be 
divided  between  the  up  and  down  strokes.     An  effort  is 
sometimes  made  in  the  construction  of  the  pump  to  divide 
the  labor  between  the  two  strokes  and  one  of  the  methods 
employed  is  represented  in  the  double  acting  pump  of  Fig. 
260.     In  this  pump  there  are  two  cylinders,  the  upper  one 
without  a  valve  and  having  one-half  the  cross-section  of 
the  lower  one.     With  this  arrangement,  when  the  piston  is 


Double  Acting  Pump. 


551 


raised  one-half  of  the  water  passes  into  the  discharge  pipe, 
while  the  other  one-half  rises  into  the  smaller  cylinder 
which,  with  the  down 
stroke,  ninst  be  forced  out 
through  the  discharge  pipe, 
in  this  way  dividing  the  la- 
bor between  the  two  strokes 
of  the  pump.  In  other 
forms  of  pumps  the  same 
result  is  accomplished  by 
arranging  an  air  chamber 
in  connection  with  the  cyl- 
inder in  such  a  way  that, 
when  the  up  stroke  is  made, 
a  part  of  the  water  rises 
into  the  air  chamber,  com- 
pressing the  air  to  such  an 
extent  that  while  the  down 
stroke  of  the  piston  is  being 
made  the  air  expands,  forc- 
ing the  water  out,  thus  se- 
curing double  action. 

698.  Proper  Place  for  the 

Cylinder  in  the  Well The 

maximum  hight  to  which 
the  air  pressure  can  sustain 
a  column  of  water  at  sea 
level  is  only  about  34  feet. 
But  the  imperfect  action  of 
the  best  suction  pumps,  to- 
gether with  the  pressure 
exerted  by  the  water  vapor 
and  the  air  escaping  from 

the     Water     when      a     high       FIG.  260. -Double  acting  suction  pump 

vacuum  is    produced    over 

it,  makes  it  impracticable  to  have  the  piston  placed  more 

than  16  to  20  feet  above  water  in  the  well. 


552  Farm  Mechanics. 

The  best  place  for  the  cyclinder  in  any  well,  if  there  is 
a  sufficient  depth  of  water  to  permit  of  it,  is  several  feet  be- 
low the  level  of  the  water.  When  the  cvlinder  is  placed  be- 
neath the  water  it  is  where  it  will  always  be  "primed" 
and  where  there  is  little  danger  of  lowering  the  water  by 
pumping  to  a  level  at  which  the  pump  works  imperfectly. 
The  general  rule  to  follow  then  is  to  place  the  cylinder 
as  low  in  the  well  as  practicable,  or  so  far  below  the  sur- 
face of  the  water  that  it  will  always  be  covered. 

699.  Hydraulic  Ram. — Where  the  conditions  are  favor- 
able for  the  use  of  the  hydraulic  ram  for  domestic  water 
supply  it  is  one  of  the  cheapest,  most  satisfactory  and 
efficient  means  yet  devised  for  lifting  water. 

The  hydraulic  ram  consists  of  (1)  a  drive  pipe,  (2) 
an  air  chamber,  (3)  an  impetus  valve,  (4)  a  discharge  pipe 
and  (5)  a  discharge  valve.  The  principle  of  the  hydraulic 
ram  is  that  of  using  the  inertia  or  momentum  of  a  large 
volume  of  water  to  raise  a  fraction  of  the  same  water  to 
the  desired  hight.  The  water  is  allowed  to  flow  through 
the  drive  pipe  until  it  acquires  velocity  enough  to  close 
the  impetus  valve  and  this  immediately  stops  the  column 
of  water  in  the  drive  pipe,  causing  it  to  act  like  a  water 
hammer  to  force  open  the  discharge  valve  leading  into 
the  air  chamber,  compressing  the  air  by  means  of  a  portion 
of  the  water  which  is  driven  in.  As  soon  as  the  column 
of  water  in  the  drive  pipe  is  brought  to  rest  the  impetus 
valve  falls  down  of  its  own  weight  and  this  allows  the 
water  in  the  drive  pipe  to  flow  at  full  velocity  again  until 
it  is  finally  moving  fast  enough  to  close  it  once  more,  when 
the  sudden  stopping  forces  another  charge  into  the  air 
chamber.  In  this  way  the  steps  are  continually  repeated, 
thus  maintaining  a  steady  supply  of  water,  the  compressed 
air  forcing  the  water  into  the  discharge  pipe  leading  to 
where  the  water  is  desired. 

The  hydraulic  ram  can  be  used  where  there  is  only 
a  comparatively  small  fall,  of  even  two  or  three  feet,  but 
where  it  is  used  to  supply  drinking  water  from  a  spring  the 


Hydraulic  Earn.  553 

chief  difficulty  is  in  arranging  to  convey  the  water  in  such 
a  way  that  it  will  not  become  too  warm,  even  if  the  pipe 
is  carried  3  or  4  feet  under  ground  where  it  would  be  safe 
against  frost  in  winter.  The  ground  becomes  warm 
enough  in  summer  time  to  leave  the  temperature  unsatis- 
factory if  the  water  must  be  carried  any  considerable 
distance.  The  water  may  be  carried  in  this  way  to  any 
distance  and  any  hight  but  the  per  cent,  of  the  stream  con- 
veyed decreases  with  both  the  hight  and  the  distance. 


PRINCIPLES  OE  WEATHER  FORECASTING, 


CHAPTEK    XXIV. 
THE  ATMOSPHERE. 

As  the  life  processes  of  all  plants  and  animals  are  de- 
pendent upon  the  air,  and  are  greatly  influenced  by  changes 
in  it,  it  is  eminently  proper  that  the  atmosphere  and  its 
changes  should  be  considered  in  their  relations  to  a<mcul- 

o  o 

ture.  From  the  standpoint  of  food  supply  the  clover  crop, 
for  example,  containing  at  maturity  70  per  cent,  of  water, 
has — directly  or  indirectly — obtained  all  but  its  ash  in- 
gredients from  the  atmosphere.  The  water  is  brought  to 
the  soil  as  rain,  the  carbon  comes  from  the  carbon  dioxide 
and  the  nitrogen  is  obtained  from  the  soil  air  by  the  free- 
nitrogen-fixing  bacteria.  The  relations  stand 

Water  from  the  atmosphere  as  rain 70 .00  per  cent. 

Nitrofren  from  the  soLl-air 70  per  cent. 

CarboD   and  oxygen   from   the   atmosphere   as  rain  and  carbon 

dioxide 26.57  per  cent. 

Ash  ingredients  from  the  soil 2.73  per  cent. 

Total  100. 00  per  cent. 

Thus  97.27  per  cent,  of  the  plant  food  is  derived  from 
the  constituents  of  the  atmosphere,  either  directly  or  in- 
directly. 

700.  Relation  of  the  Atmosphere  to  the  Earth. — The  earth 
consists  of  three  concentric  spheres,  (1)  at  the  center,  the 
solid,  or  earth-sphere;  (2)  surrounding  this  is  the  liquid  or 


Relations  of  ike  Life  Zoiie.  555 

water-sphere,    (3)    and  outside  of  all  is   the  gas   or   air 
sphere.     These  have  been  named — • 

1.  Geosphere. 

2.  Hydrosphere. 

3.  Atmosphere. 

701.  Interpenetration  of  the  Three  Spheres. — The  mate- 
rials of  the  three  spheres  are  neither  entirely  separated  from 
one  another  nor  stationary.     Beneath  the  oceans  and  be- 
neath the  surface  of  the  continents  the  solid  earth  is  per- 
meated by  water.     Even  under  desert  skies  there  may  be 
wells  and  the  soil  contains  moisture.     With  the  water,  too, 
goes  more  or  less  of  air  from  the  atmosphere ;  the  fishes 
of  the  oceans  and  lakes  find  air  to  breathe  wherever  they  go 
and  the  spaces  in  rock  and  soil  not  occupied  by  water  are 
filled  with  air.     Floating  in  the  water  and  drifting  in  the 
atmosphere  even  at  great  hights  are  solid  particles  of  silt 
and  dust  broken  from  the  earth-sphere,  and  nowhere  is  air 
so  dry  that  it  contains  no  moisture. 

Drifted  by  the  currents  of  air  and  water  on  land  and  at 
sea  solid  particles  are  continually  being  moved  from  place 
to  place.  The  water  of  the  ocean,  of  the  lakes  or  of  the  at- 
mosphere is  never  at  rest,  neither  is  that  which  has  pene- 
trated the  solid  crust  of  the  earth.  So,  too,  the  air  of  the 
atmosphere,  of  the  water  and  of  the  soil  is  continually 
changing  and  upon  the  rate  of  these  changes  depends  the 
well  being  of  plant  and  animal  life. 

702.  Relation  of  the  life  Zone  to  the  Three  Spheres. — The 
living  forms  of  the  earth  make  their  homes  in  the  bottom 
of  the  atmosphere  and  in  the  top  of  the  water  sphere  or  of 
the  earth  sphere.     This  relation  is  necessitated  by  the  fact 
that  all  living  forms  derive  their  food  from  the  air,  from 
the  water,  and  either  from  the  earth  or  from  other  forms 
which  take  their  ash  ingredients  from  the  earth.     This  re- 
lation is  further  necessitated  by  the  fact  that  all  living 
forms  must  dwell  where  they  can  have  a  certain  amount  of 
direct  sunshine  or  else  where  they  can  live    upon  other 


556  Principles  of  Weather  Forecasting. 

forms  which  depend  upon  it,  for  this  is  the  moving  power 
of  the  world  and  all  life  implies  motion.  Deep  in  the 
solid  earth  no  life  exists.  In  the  greatest  depths  of  the 
ocean,  where  the  air  changes  are  slow  and  where  little  or  no 
light  can  come,  life  is  nearly  absent ;  and  high  in  the  atmos- 
phere only  latent  forms  of  life,  like  the  spores  and  germs 
of  microscopic  forms  are  drifted  by  the  winds. 

In  brief  the  life  zone  is  that  portion  of  the  three  spheres 
where  the  largest  amount  of  sunshine  is  transformed  into 
heat  motion  and  -therefore  where  there  is  the  largest 
amount  of  energy  available  for  the  use  of  plants  and  ani- 
mals. 

703.  Depth  of  the  Atmosphere. — We  are  living  at  the  bot- 
tom of  an  ocean  of  air  whose  depth  is  at  present  unknown. 
Judging  from  the  rate  of  decrease  of  pressure,  as  measured 
by  the  barometer,  its  depth  would  be  placed  at  something 
less  than  50  miles,  for  at  30  miles,  could  an  instrument  be 
placed  at  that  level,  it  is  calculated  that  its  reading  would 
be  only  .005  of  an  inch  of  mercury.  Observations  which 
have  been  made  upon  the  hight  at  which  shooting  stars  or 
meteors  become  visible  shows  that  this  is  even  more  than 
100  miles  and  it  is  believed  that  these  bodies  become  visible 
only  after  they  have  traversed  enough  of  our  atmosphere 
to  develop  sufficient  heat  by  friction  and  compression  to 
make  them  white-hot;  and  although  the  velocity  of  these 
bodies  is  very  great  yet  the  upper  air  is  so  rarified  they 
must  pass  through  great  depths  before  sufficient  heat  can 
be  developed  to  make  them  white-hot.  From  these  consid- 
erations it  appears  likely  that  air  may  be  found  at  hights 
even  exceeding  500  miles. 

704.  Composition  of  the  Atmosphere. — The  air  at  differ- 
ent times  and  in  different  places  contains  a  great  variety 
of  gases  and  volatile  products  but  there  are  certain  con- 
stituents which  are  found  everywhere  in  the  explored  reg- 
ions and  in  pretty  constant  ratios.  These  are,  for  dry  air : 

1.  Nitrogen,  forming  about  77.18  per  cent,  by  volume. 


Composition  of  the  Atmosphere.  557 

2.  Oxygen,  forming  about  20.61  per  cent,  by  volume. 

3.  Water  vapor,  forming  about  1.40  per  cent,  by  vol- 
ume. 

4.  Argon,  forming  about  .78  per  cent,  by  volume. 

5.  Carbon  dioxide,  forming  about  .03  per  cent,  by  vol- 
ume. I 

Besides  these  ingredients  there  are  usually  present  in  the 
air  small  amounts  of  ammonia  and  of  nitric  acid,  which 
are  brought  down  with  the  rains  to  the  extent  of  3.37 
pounds  per  acre  per  annum  at  Rothamsteacl,  England; 
1.74  pounds  at  Lincoln,  New  Zealand ;  and  3.77  pounds  in 
the  Barbadoes  Islands. 

Oxygen  often  occurs  in  the  allotropic  form  of  ozone, 
which  is  much  more  active  as  an  oxidizing  agent  than  the 
ordinary  condition. 

705.  Materials  Mechanically  Suspended  in  the  Atmos- 
phere.— In  the  gaseous  body  of  the  atmosphere  there  are 
always  mechanically  suspended  varying  amounts  of  solid 
and  liquid  particles  and  bodies.  These  are : 

1.  Inorganic  dust  grains  or  soil  particles. 

2.  Organic  dust  fragments. 

3.  Microscopic  germs  and  spores. 

4.  Pollen  grains  from  various  plants. 

5.  Snow  or  water  crystals. 

6.  Water  particles  in  cloud  forms. 


PARTS  PLAYED  BY  THE  DIFFERENT  INGREDIENTS. 

The  atmosphere  as  a  whole,  in  its  relation  to  living 
forms,  plays  the  important  function  of  an  equalizer  of  tem- 
perature, preventing  the  occurrence  of  such  excessively 
high  and  extremely  low  degrees  as  would  otherwise  be  pro- 
duced when  the  sun  is  above  or  below  the  horizon. 

706.  Oxygen — Oxygen  is  essential  to  both  plants  and 
animals,  it  being  indispensable  to  the  activities  of  the  proto- 


558  Principles  of  Weather  Forecasting. 

plasm  of  living  cells,  whether  this  be  in  the  root,  stem  or 
leaf  of  plants  or  in  the  tissues  of  animals.  In  the  develop- 
ment of  muscular  and  nervous  energy  large  quantities  are 
used  by  the  animal  kingdom,  and  other  large  volumes  are 
used  by  man  with  fuel  as  a  source  of  power  and  heat. 

707.  Nitrogen. — The  nitrogen  of  the  atmosphere  is  pri- 
marily the   source   of   all   nitrogen   compounds   of  living 
forms;  and  by  its  dilution  of  all  the  other  ingredients  it 
modifies  their  physiological  effects. 

708.  Water. — Moisture  in  the  atmosphere  greatly  influ- 
ences the  temperature  of  the  earth's  surface,  as  it  is  very 
opaque  to  dark  heat  waves  radiated  back  into  space.     The 
frosts  forming  under  clear  skies  and  the  absence  of  them 
when  the  air  is  damp  are  evidence  of  this  influence.     But 
the  chief  function  of  water  is  found  in  its  large  movement 
to  the  land  in  the  form  of  rain  and  snow  and  its  return 
from  the  fields  through  springs  and  rivers  to  the  seas.     As 
it  falls  it  is  food  for  plants  and  drink  for  animals,  as  it  re- 
turns it  carries  away  soluble  salts  which,  if  left,  would  de- 
velop sterile  "alkali"  lands. 

709.  Dust. — The  dust  particles  give  to  the  sky  its  blue 
color  and  by  their  radiation  of  heat  into  space  become  cold 
centers  upon  which  moisture  condenses  and  snow  flakes 
form.     In  this  way  they  greatly  influence  the  precipita- 
tion, making  it  less  violent  than  it  might  otherwise  be. 

710.  Carbon  Dioxide. — Carbon  dioxide  is  the  source  of 
all  the  carbon  entering  into  the  constitution  of  the  tissues 
of  both  plants  and  animals,  and  it  is  a  constituent  of  the 
great  majority  of  feeding  stuffs  and  of  most  organic  com- 
pounds. 

From  recent  investigations  it  is  held  that  carbon  dioxide 
plays  an  important  part,  with  water,  in  lessening  the 
transparency  of  the  atmosphere  to  dark  heat  rays  radiating 
from  the  earth  into  space,  and  in  this  way  holds  our  tern- 


Pressure  of  the  Atmosphere. 


559 


peraturo  much  higher  than  it  could  be  with  this  gas  absent; 
and  Chamberlin  has  proposed  the  working  hypothesis  that 
long  period  changes  in  the  amount  of  carbon  dioxide  in 
the  atmosphere  may  be  the  cause  of  the  recurrent  glacial 
periods  to  which  the  earth  has  been  subjected. 

711.  Pressure  of  the  Atmosphere. — The  air,  like  all  other 
substances,  has  weight,  and  this  weight  causes  it  to  exert 
pressure  proportional  to  the  amount  above  a  place.  Its 
mean  pressure  at  sea  level  is  equal  to  14.73  pounds  per 
square  inch.  A  cubic  foot  of  air  at  this  pressure  and  at  a 
temperature  of  62°  F.  weighs  about  .08  pounds,  100  cubic 
feet  would  weigh  8  pounds,  and  10,000  cubic  feet  807.28 
pounds.  The  air  of  a  stable  50x50  feet,  10  feet  high, 
weighs  a  ton. 

As  the  hight  increases  above  sea  level  the  amount  of  air 
to  exert  pressure  is  less,  the  weight  of  a  cubic  foot  becomes 
less  and  it  is  necessary  to  breathe  a  larger  volume  to  supply 
the  system  with  the  same  amount  of  oxygen.  In  the  next 
table  are  given  in  round  numbers  the  hights  above  the  sea 
at  which  the  pressure  would  fall  from  30  to  16  inches  and 
the  hight  to  which  these  pressures  would  sustain  a  column 
of  water,  could  a  perfect  vacuum  be  maintained. 


Hight  above  sea  level. 

Barometric    pressure. 

Hight  of  water  column.  ' 

0 

39  inches. 

34.0  feet. 

l,80i)  feet. 

& 

31.7 

a.fcoo 

26 

29.4 

5,900 

24 

27.2 

8,200 

22 

24.9 

10,000 

20 

22.6 

13,200 

18 

20.4 

16,000 

16 

18.1 

712.  Applications  of  Atmospheric  Pressure. — The  most 
general  application  of  atmospheric  pressure  by  the  animal 
world  is  in  bringing  air  into  their  respiratory  organs. 
Where  animals  are  constituted  so  as  to  take  advantage  of 
this,  a  reduction  of  pressure  is  made  about  the  lungs,  as  in 
raising  the  ribs  and  lowering  the  diaphragm,  and  then  the 
greater  pressure  of  the  air  outside  expands  them  and  causes 
a  fresh  supply  to  enter  and  fill  the  space. 


560  Principles  of  Weather  Forecasting. 

In  drinking  and  in  sucking  animals  take  advantage  of 
the  air  pressure  to  perform  these  operations,  which  would 
be  impossible  without  the  pressure,  and  difficult  where  the 
pressure  is  small. 

Even  in  eating,  animals  with  lips  and  cheeks  take  ad- 
vantage of  air  pressure  to  force  the  food  from  between  the 
teeth  after  it  has  been  masticated,  and  a  man  would  make 
awkward  work  eating  for  the  first  time  in  a  vacuum. 

In  the  common  suction  pump  and  the  siphon  air  pres- 
sure is  an  essential  factor,  as  it  is  in  the  low  pressure  steam 
engine. 

All  of  the  machines  invented  for  milking  cows  develop 
a  vacuum  and  depend  upon  atmospheric  pressure  to  force 
the  milk  from  the  udder. 

713.  Temperature  of  the  Atmosphere. — The  air  is  warmed 
in  three  ways :  first,  and  chiefly,  by  contact  with  the  earth's 
surface  and  with  solid  objects  upon  it,  this  heating  giving 
rise  to  ascending  currents  of  warm  and  descending  ones  of 
cold  air.  Second,  by  dark  heat  radiations  outward,  which 
are  absorbed  by  the  atmosphere  as  water  absorbs  light. 
Third,  by  absorption  of  the  direct  rays  from  the  sun  on 
their  way  to  the  earth's  surface. 

When  air  descends  from  a  higher  to  a  lower  level  the 
pressure  upon  it  becomes  greater  and  its  volume  is  reduced. 
This  reduction  of  volume  causes  it  to  have  a  hisrhf-r  tem- 
perature, and  so  if  the  air  rises  it  expands,  and  this  expan- 
sion results  in  lowering  tin  temperature.  A  rise  or  fall 
of  100  feet  causes  a  change  of  temperature  of  .55°  F.  in 
dry  air. 

If  dry  air  crosses  a  mountain  range  and  falls  2,000  feet 
its  temperature  is  raised  11°  F. 

When  moisture  is  condensed  or  frozen  in  the  atmos- 
phere the  air  temperature  is  raised  by  the  heat  generated 
during  condensation.  So,  too,  if  water  is  evaporated  in 
the  air,  or  snow  melts,  the  temperature  falls.  This  is  why 
the  weather  is  always  warmer  in  winter  when  it  snows,  and 
cooler  after  showers. 


CHAPTEK    XXV. 
MOVEMENTS  OF  THE  ATMOSPHERE. 

714.  Primary  Cause  of  Winds — Winds  usuallybegin  in 
one  of  two  ways,  represented  in  Fig.  261.     In  the  lower 


FIG.  261. — Diagram  showing  the  origin  of  wind  movements. 

part  of  the  figure  the  white  portion  represents  a  region 
where  the  air  is  expanding.  When  this  occurs  the  lo\yor 
and  heavier  air  is  carried  upward  nnd  hmfight  alongside 


562  Principles  of  Weather  Forecasting. 

that  which  is  lighter ;  then  because  of  the  resulting  unbal- 
anced pressure  the  air  above  flows  over  outward,  as  repre- 
sented by  the  upper  arrows.  But  as  soon  as  some  air  has 
left  the  expanding  area  the  whole  column  is  made  lighter, 
while  the  shaded  areas  become  heavier  from  the  added 
amount,  and  there  is  an  unbalanced  condition  through  the 
whole  hight.  At  the  center  there  is  an  area  of  low  pres- 
sure and  around  it  one  of  high,  hence  the  winds  set  inward 
from  all  sides  at  the  surface  and  outward  above,  as  shown 
by  the  arrows  in  the  diagram,  and  we  have  what  is  called 
a  cyclonic  system  of  winds,  where  the  currents  are  mov- 
ing inward  toward  a  low  pressure  area  below  and  outward 
above  toward  one  that  is  higher. 

If  the  central  area  is  one  where  the  air  is  contracting  and 
becoming  denser  then  air  will  flow  in  upon  it  from  above, 
as  shown  in  the  upper  part  of  the  diagram  of  Fig.  261.  But 
as  soon  as  air  moves  from  the  surrounding  area  upon  the 
central  one  the  inner  region  becomes  a  high  area,  where 
the  greater  pressure  forces  the  air  outward  below  and  in- 
ward above.  Such  a  wind  system  as  this  has  been  named 
an  anticyclone. 


GENERAL   CIRCULATION   OF   THE   ATMOSPHERE. 

715.  The  World  System  of  Winds. — In  the  region  of  the 
equator,  where  the  heat  is  greatest,  the  air  is  continually 
expanding,  and  flowing  toward  the  poles  above ;  this  makes 
the  pressure  greater  on  either  side,  resulting  in  surface 
winds  setting  toward  the  equator,  as  represented  in  ver- 
tical section  in  Fig.  262,  which  it  will  be  seen  is  essentially 
the  cyclonic  system  of  Fig.  261.  Farther  toward  the  poles 
on  either  side,  where  the  overflowing  air  from  the  equator 
accumulates,  a  high  pressure  belt  is  developed,  from  under 
which  part  of  the  air  flows  toward  the  equator  below  and 
another  toward  the  poles ;  these  are  the  tropical  high  pres- 
sure belts. 

At  the  poles,  where  the  air  is  continually  cooling,  it  is 


Movements  of  the  Atmosphere. 


563 


steadily  descending  and  flowing  outward  below,  maintain- 
ing an  anti-cyclonic  system  of  winds  like  that  of  the  upper 
part  of  Fig.  261.  Between  the  high  area  at  the  poles  and 
the  tropical  high  pressure  belts,  where  the  two  systems  of 


FIG.   262.— Diagram    of    the    World     system    of    winds.    (Adapted     from 

Ferrel.) 

surface  winds  meet,  there  is,  in  the  judgment  of  Ferrel,  a 
tendency  to  develop  a  third  or  polar  calm  belt,  over  which 
the  air  rises  to  return  as  an  upper  current  to  the  tropical 
calm  belts,  or  else  back  again  to  the  poles. 

716.  Wind  Zones. — There  is  thus  a  tendency  for  the  sur- 
face winds  of  the  globe  to  divide  into  six  zones,  separated 
by  five  calm  belts, — two  tropical  or  trade  wind  zones,  two 
temperate  or  anti-trade  wind  zones  and  two  polar  zones,  as 


564  Principles  of  Weather  Forecasting. 

represented  in  Fig.  262.  In  the  two  tropical  and  two  polar 
zones  the  winds  move  toward  the  equator,  while  in  the  two 
temperate  zones  they  move  away  from  the  equator. 

Above  the  earth's  surface  the  directions  of  the  wind  are 
the  reverse  of  those  found  below,  that  is,  over  the  tropics 
and  in  the  polar  regions  the  upper  winds  move  toward  the 
poles,  while  over  the  temperate  zones  the  upper  winds  are 
toward  the  equator. 

717.  Direction  of  Wind  Modified  by  Form  and  Eotation  of 
the  Earth. — The  shape  of  the  earth  and  its  rotation  upon 
its  axis  greatly  modify  the  direction  of  winds.     The  rota- 
tional velocity  of  the  earth's  surface  at  the  equator  is  about 
1,000  miles  per  hour  toward  the  east.     As  the  distance  to- 
ward the  poles  increases  the  eastward  velocity  decreases. 
When  therefore  air  moves  toward  the  poles  it  travels  east- 
ward faster  than  the  land  it  approaches  and  hence  blows 
from  a  westerly  toward  an  easterly  direction. 

On  the  other  hand  air  moving  toward  the  equator  passes 
over  land  traveling  eastward  more  rapidly  than  it  does,  and 
hence  these  winds  fall  behind  and  appear  to  blow  from 
some  easterly  toward  some  westerly  direction. 

The  surface  winds  in  the  tropics  and  polar  regions  are 
northeast  or  southeast,  according  to  which  hemisphere 
they  are  in,  while  the  upper  winds  of  the  same  zones  have 
the  reverse  direction.  In  the  temperate  zones  the  winds 
are  southwest  or  northwest  at  the  surface  and  northeast 
or  southeast  above,  according  as  they  are  north  or  south 
of  the  equator. 

718.  Character  of  the  Winds — Winds   blowing   toward 
the  equator  or  descending  from  the  upper  regions  have  a 
tendency  to  be  dry  and  to  maintain  a  clear  sky.     On  the 
other  hand  winds  moving  toward  the  poles,  or  rising  to 
greater  altitudes,  tend  to  become  more  and  more  nearly  sat- 
urated with  moisture  and  hence  to  produce  cloudy  skies 
and  precipitation. 

The  reasons  for  these  relations  are  found  in  the  fact  that 


Movements  of  the  Atmosphere.  565 

air  rising  or  moving  toward  the  poles  is  passing  toward  a 
colder  region.  Lowering  the  temperature  of  the  air,  with- 
out changing  the  amount  of  moisture  in  it  makes  it  more 
nearly  saturated,  while  raising  the  temperature  without 
changing  the  amount  of  moisture  makes  the  air  dryer. 

Besides  this,  air  is  cooled  by  expansion  and  warmed  by 
compression,  and  on  these  accounts  ascending  currents  tend 
to  become  damp  and  descending  air  more  dry. 

719.  Weather  of  the  Wind  Zones. — It  will  be  evident 
from  718  that,  so  far  as  the  world  system  of  winds  are  not 
interfered  with  by  local  conditions,  they  must  give  to  the 
countries  over  which  they  blow  characteristic  types  of 
weather.  Under  the  tropical  high  pressure  calm  belts, 
where  the  air  is  descending,  and  for  a  long  distance  to  the 
south  and  a  shorter  one  to  the  north,  there  must  be  a  region 
of  clear  skies  and  dry  weather,  and  it  is  under  these  two 
zones  that  the  deserts  of  the  world  are  found. 

In  the  polar  regions  also  the  cloudiness  and  precipita- 
tion are  relatively  small  for  the  same  reason. 

But  at  the  equator,  where  large  volumes  of  air  are  ris- 
ing into  the  upper  regions  and  after  doing  so  pass  toward 
the  poles,  the  air  having  become  very  moist  before  rising, 
quickly  becomes  saturated  and  throws  back  to  the  earth 
large  amounts  of  rain.  The  heaviest  rainfalls  of  the 
world  are  under  the  equatorial  calm  belt  of  ascending  cur- 
rents. 

In  the  two  temperate  zones  also,  where  the  winds  cool 
as  they  move  northward,  frequent  rains  and  showers  and 
much  cloudy  weather  are  the  rule. 

There  is  thus  a  tendency  for  the  systems  of  world  winds 
to  develop  three  rainy  or  cloudy  zones  and  four  clear 
weather  or  dry  zones.  The  dry  zones  are  under  the  tropics 
and  about  the  poles ;  the  wet  and  cloudy  zones  are  under  the 
equator  and  between  the  tropical  and  polar  circles  of  both 
hemispheres. 

720.  Shifting  of  the  Zones — Because  the  vertical  rays 
36, 


566  Principles  of  Weather  Forecasting. 

of  the  sun  fall  alternately  23!/2  degrees  north  and  south 
of  the  equator,  the  regions  of  greatest  heating  must  also 
move  north  and  south  with  the  apparent  shifting  of  the 
sun,  and  this  causes  the  equatorial  and  tropical  calm  belts 
to  move  north  and  south.  As  a  result  of  this  shifting  there 
is  a  tendency  to  develop  two  rainy  and  two  dry  seasons  each 
year  in  the  regions  over  which  the  calm  belts  travel  twice. 


CONTINENTAL  WINDS. 

721.  Continents  Disturb  the  World  System  of  Winds  and 
Weather. — The  small  specific  heat  of  the  land,  its  opaque 
nature  and  the  absence  of  currents  of  all  kinds  in  it  cause 
the  land  surface  to  warm  rapidly  in  the  day  and  during 
summer,  and  to  cool  rapidly  at  night  and  during  the  win- 
ter. On  the  other  hand  the  transparency  of  the  oceans, 
which  allows  the  sunshine  to  be  distributed  through  a  great 
depth  of  water ;  their  high  specific  heat  and  the  horizontal 
and  vertical  currents  to  which  they  are  subject,  all  con- 
spire to  make  the  oceans,  relative  to  the  lands  in  the  same 
latitude,  warm  in  winter  and  cool  in  summer. 

During  the  long  days  of  summer  and  short  nights,  in 
high  latitudes,  the  land  becomes  much  warmer  than  the 
water  and  tends  to  develop  ascending  currents  and  a  low 
air  pressure,  causing  the  winds  to  tend  to  blow  toward  the 
land  at  the  surface  and  away  from  the  land  above  in  sum- 
mer ;  but  in  winter,  when  the  nights  are  long  and  the  days 
short,  the  ground  becomes  very  cold  and  the  air  contracts, 
causing  the  upper  air  to  blow  in  over  the  continents  above, 
thus  developing  high  pressure,  which  forces  the  surface 
winds  to  move  from  the  land  toward  the  ocean  in  winter. 

There  is  therefore  a  tendency  for  the  weather  of  conti- 
nents to  be  rainy  and  cloudy  in  summer  and  dry  and  sunny 
in  winter,  and  for  the  oceans  to  be  dry  and  sunny  in  sum- 
mer and  wet  and  cloudy  in  winter.  This  is  a  very  for- 
tunate relation,  because  it  diminishes  the  evaporation  on 
the  land  and  increases  that  on  the  ocean  and  thus  makes 


Continental  Winds.  567 

the  rainfall  heaviest  at  just  the  season  when  crops  need 
most  water. 

722.  The  World  Winds  of  January — The  prevailing 
winds  of  the  world,  as  they  are  observed  during  the  month 
of  January,  are  represented  in  Fig.  263,  the  lines  of  black 
circles  showing  where  the  modified  tropical  high  pressure 
calm  belts  are  situated,  and  the  light  circles  showing  where 
the  equatorial  calm  belt  and  other  low  pressure  areas  are. 
In  the  southern  hemisphere,  where  it  is  summer,  and 
where  the  amount  of  land  is  small  compared  with  the 
water,  the  tropical  high  pressure  calm  belt  is  crowded  to- 
ward the  pole  on  the  land  and  the  air  is  heaped  up  on  the 
water,  and  the  arrows  show  that  the  wind  blows  toward 
the  land ;  but  in  the  northern  hemisphere,  where  it  is  win- 
ter, and  where  the  amount  of  land  is  much  larger,  it  is 
also  drawn  toward  the  poles  by  the  extreme  cold  of  the 
land,  while  a  low  area  is  formed  over  each  of  the  northern 
oceans.  The  wind  blows  off  both  continents  onto  the  two 
oceans  and  there  are  upper  currents  tending  toward  the 
land  from  the  low  areas. 

The  equatorial  calm  belt  is  farther  south  everywhere, 
but  especially  so  over  South  America  and  over  Africa  and 
Australia,  where  the  land  becomes  warmest. 

723.  World  Winds  in  July — At  this  time  of  the  year, 
when  the  northern  hemisphere  has  the  vertical  rays  of  the 
sun  and  the  longest  days,  the  large  masses  of  land  have  be- 
come over-heated,  the  equatorial  calm  belt  has  been  drawn 
northward  and  expanded  into  wide  continental  low  areas, 
crowding  the  high  pressure  belt  of  the  Tropic  of  Cancer 
upon  the  Atlantic  and  Pacific  oceans,  as  represented  in 
Fig.  264.  The  warm  air  rising  over  the  continents  and 
flowing  over  upon  the  oceans  makes  high  pressure  there 
and  low  pressure  over  the  land,  and  this  brings  surface 
winds  and  moisture  from  the  sea,  giving  rains  to  the  land 
in  the  summer  season, 


568 


Principles  of  Weather  Forecasting. 


tr/W* 


Continental  Winds. 


569 


570  Principles  of  Weather  Forecasting. 

South  of  the  equator,  where  it  is  winter,  the  high  pres- 
sure calm  belt  has  moved  nearer  the  equator  so  that  the  air 
is  blowing  off  the  three  continents  and  they  are  experienc- 
ing their  dry  season. 

724.  Monsoon  Winds — Where  the  world  system  of  winds 
is  so  strongly  influenced  by  the  land  areas  as  is  the  case 
notably  in  the  region  of  the  Indian  Ocean  they  have  been 
given  the  special  name  of  monsoons,  and  these  give  to  In- 
dia its  rainy  season,  when  they  blow  from  the  ocean,  and 
its  dry  season,  when  they  blow  from  the  land. 


ORDINARY    STORMS. 

Besides  the  world  system  of  winds,  which  have  been  de- 
scribed, and  the  continental  winds  with  their  intensified 
forms  called  monsoons,  which  change  with  the  seasons, 
there  are  others  of  smaller  magnitude  and  shorter  duration 
which  give  rise  to  our  ordinary  storms  and  the  still  more 
local  tornadoes  and  thunder  storms  which  are  associated 
with  them.  These  are  technically  called  cyclones  or  cy- 
clonic storms. 

725.  Cyclones. — Most    of    the    rainfall    of    temperate 
climates  and  much  of  that  which  falls  between  the  tropics 
and  the  equatorial  calm  belt,  occurs  during  the  passage 
of  these  cyclonic  systems  of  wind  movement,  represented 
in  Figs.  265  and  266. 

In  these  winds  the  surface  air  moves  spirally  about  a 
center,  going  to  the  east  as  it  passes  toward  the  poles  and 
to  the  west  of  the  center  when  it  comes  toward  the  equator. 
Air  coming  from  the  eastward  of  a  cyclonic  center  always 
passes  to  the  polar  side,  while  that  coming  from  the  west 
always  passes  to  the  equatorial  side. 

726.  Cause  of  Wind  Directions  in  Ordinary  Storms. — The 
cause  of  the  wind  directions  in  ordinary  storms  is  the  same 


Ordinary  Storms.  571 

as  that  of  the  direction  of  the  general  earth  currents,  that 
is, — the  form  and  rotation  of  the  earth.  As  the  air  leaves 
the  equator  it  passes  over  land  moving  eastward  slower 
than  it  and  hence  outruns,  appearing  to  blow  from  the 


FIG.  265.— Diagram  of  surface  winds  in  a  typical  cyclone.    (After  Ferrel.) 

S.  W.  toward  the  N.  E.  in  the  northern  hemisphere,  and 
from  the  N".  W.  toward  the  S.  E.  in  the  southern  hemi- 
sphere. If  it  approaches  the  equator  it  travels  over  land 
moving  eastward  faster  than  it  does  and  hence  appears  to 
come  from  the  N".  E.  in  the  northern  hemisphere  and  from 
the  S.  E.  in  the  southern. 

Where  the  wind  approaches  the  center  from  the  east  it 
can  only  do  so  by  having  its  eastward  motion  with  the  earth 
made  slower  than  the  earth's  surface  in  the  same  latitude ; 


572 


Principles  of  Weather  Forecasting. 


while  if  it  approaches  the  center  from  the  west  it  can  only 
do  so  by  traveling  eastward  faster  than  the  earth  itself  and 
these  changes  in  velocity  cause  winds  from  the  west  to 
move  toward  the  equator  side  of  the  storm  center,  while 
those  from  the  east  always  go  to  the  polar  side.  The  effect 
is  the  same  as  would  result  from  checking  or  increasing 


FIG.  266.— Diagram  of  upper  winds  in  a  typical  cyclone.    (After  Ferrel.) 

the  rate  of  rotation  of  the  earth  upon  its  axis.  Making 
it  rotate  faster  would  throw  the  air  and  water  also  toward 
the  equator,  while  slackening  its  speed  would  permit  both 
air  and  water  to  move  toward  the  poles. 

727.  Progressive  Movements  of  Storms Cyclonic  storms 

in  all  parts  of  the  world  have  a  progressive  movement 


Ordinary  Storms. 


573 


574:  Principles  of  Weather  Forecasting. 

across  the  earth's  surface  and  the  general  direction  is  that 
of  the  prevailing  winds  of  the  part  of  the  earth  in  which 
they  are.  That  is,  in  the  temperate  zones  they  tend  to 
move  away  from  the  equator  and  toward  the  east,  while  in 
the  tropical  zones  they  tend  to  move  toward  the  equator 
and  toward  the  west. 


728.  Direction  of  Storms  in  the  United  States. — In  the 
great  majority  of  cases  the  storms  of  the  United  States 
travel  from  some  westerly  toward  some  easterly  point  and 
the  mean  direction  is  a  little  north  of  east.     Very  many 
of  these  storms  travel  for  a  time  from  the  northwest  toward 
the  southeast  until  they  near  the  longitude  of  the  Missis- 
sippi river,  when  they  very  often  turn  their  course  strongly 
to  the  northeast,  and  Fig.  267  represents  the  course  of  the 
storm  centers  as  they  traversed  the  country  during  March, 
1900,  there  being  13  of  them  in  all.     Wherever  the  storms 
of  the  United  States  originate  or  enter  the  territory  they 
nearly  all  leave  it  by  crossing  the  New  England  states. 

729.  Rate  of  Travel  of  Storms  in  the  United  States — 
There  is  a  very  wide  range  in  the  rate  at  which  the  storm 
centers  progress  across  the  United  States,  but  the  average 
is  from  26  to  30  miles  per  hour.     The  circles  in  the  paths 
of  the  several  storm  tracks  in  Fig.  267  mark  the  positions 
of  the  storm  centers  at  intervals  of  12  hours. 

730.  Diameters  of  Storms. — The  diameter  of  these  cy- 
clonic wind  systems  in  the  United  States  is  generally  from 
1,500  to  2,000  miles,  the  longest  diameter  being  usually 
from  the  southwest  to  the  northeast.     A  typical  one  of 
these  storms  is  represented  in  Fig.  268,  where  the  heavy 
lines  are  drawn  through  places  having  the  same  weight  of 
air  above  them,  while  the  dotted  lines  are  lines  of  equal 
temperature.  It  will  be  seen  that  this  wind  system  reaches 
from  north  of  the  Great  Lakes  to  well  into  Texas  and  from 
North  Dakota  to  Tennessee. 


Ordinary  Storms. 


575 


FIG.  268.— Chart  of  strongly  developed   low   area   in  the  vicinity  of  the 
Great  Lakes. 

731.  Duration  of  Ordinary  Storms. — The  length  of  time 
one  of  the  ordinary  cyclonic  storms  of  the  atmosphere  lasts 
is  very  variable.  In  some  cases  they  are  of  but  a  few  days 
duration ;  at  other  times  they  last  for  weeks  together  and  in 
that  time  travel  long  distances. 

It  is  common  for  them  to  cross  the  United  States,  the 
North  Atlantic  and  the  whole  of  Europe ;  and  one,  unusual 
at  least  in  the  completeness  of  its  known  history,  has  been 
followed  from  the  vicinity  of  the  Philippine  Islands, 
across  the  Pacific,  across  North  America  and  the  North 
Atlantic;  across  Europe  and  well  on  toward  the  central 
portion  of  Siberia,  where  lack  of  sufficient  observations 
prevented  following  it  farther. 


732.  Eelation  of  the  Region  of  Precipitation  to  the  Storm 
Center. — The  region  over  which  rain  or  snow  falls  during 


576 


Principles  of  Weather  Forecasting. 


the  passage  of  cyclones  across  the  United  States  lies  usu- 
ally in  advance  of  the  central  LOW,  much  as  represented 
by  the  heavily  shaded  area  in  the  diagram  Fig.  269,  and 
at  a  distance  of  200  to  700  miles  from  the  center. 

In  this  area  the  precipitation  is  most  continuous  and 
steady  over  the  eastern  and  northern  portion,  where  the 
surface  winds  range  from  S.  E.  to  !N".  E.  in  direction.  To 
the  southeast  and  south  of  the  low  center,  where  the  winds 
are  S.  and  S.  W.,  there  is  a  general  tendency  for  the  pre- 
cipitation to  occur  in  the  form  of  showers,  to  be  more  vio- 
lent in  character,  and  local  rather  than  wide  spread. 


FIG.  269.— Diagram   of  storm  area. 


733.  The  Origin  of  Ordinary  Storms. — There  is  as  yet  no 
general  agreement  among  students  of  meteorology  regard- 


Ordinary  Storms.  577 

ing  the  origin  of  cyclonic  winds  and  storms,  some  think- 
ing that  the  low  areas  are  primary  and  that  the  areas  of 
high  pressure  result  from  the  overflow  of  air  from  one  or 
more  of  these  which  overlap;  while  others  maintain  that 
the  high  areas  are  primary  and  that  the  low  areas  are  sec- 
ondary. At  the  present  time  the  former  view  is  able  to 
bring  much  the  stronger  evidence  to  its  support,  so  far  as 
the  operation  of  well  established  physical  principles  aro 
concerned,  and,  with  some  modifications,  seems  likely  in 
the  end  to  prevail. 


'CHAPTER    XXVI. 
WEATHER  CHANGES. 

The  forecasting  of  weather  changes  from  24  to  36  hours 
in  advance  is  based  upon  several  well  established  facts: 
(1)  Rainy  or  cloudy  weather  is  usually  associated  with 
areas  of  low  pressure,  about  which  the  winds  move  as  rep- 
resented in  Fig.  269.  (2)  Fair  or  clear  weather  is  usu- 
ally associated" with  regions  of  high  pressure.  (3)  Both 
low  and  high  areas  have  prevailing  dimensions  and  move 
in  the  United  States  from  the  west  toward  the  east. 

If  areas  of  low  pressure  always  had  the  same  diameter, 
and  if  they  traveled  at  the  same  rate  and  in  the  same  di- 
rection, it  would  be  possible  for  anyone  to  forecast  the 
weather  changes  with  much  certainty  12  to  36  hours  in  ad- 
vance. But  with  all  the  irregularity  of  form,  dimension, 
intensity,  rate  and  direction  of  motion,  it  is  possible  for 
even  a  local  observer  to  form  a  rational  judgment  of  the 
approach,  time  of  arrival  and  passage  of  an  ordinary 
storm.  Indeed,  it  will  seldom  happen  that  a  strongly  de- 
veloped storm  can  approach  a  locality  without  giving  sure 
signs  of  its  coming  12  to  24  hours  in  advance. 

734.  Prevailing  Winds — In  the  forecasting  of  weather 
changes  it  is  important  to  have  clearly  in  mind  the  direc- 
tion of  the  prevailing  winds  of  the  locality,  or  those  which 
are  not  due  to  the  storm  whose  approach  is  to  be  forecast. 

In  most  parts  of  the  United  States  east  of  the  Rocky 
Mountains  the  prevailing  fair  weather  winds  are  from 
some  westerly  quarter  and  they  should  be  the  southwest 
winds  of  the  general  world  and  continental  system  unless 
modified  by  local  conditions,  such  as  give  rise  to  "land  and 
sea  breezes"  or  "mountain  and  valley  winds," 


Forecasting  of  Weather  Changes.  579 

735.  locating  the  Storm  Center — When  the  weather  has 
been  for  some  time  fair  and  the  prevailing  winds  are  blow- 
ing, the  first  indication  of  an  approaching  storm  is  usually 
to  be  found  in  the  long  thread-like  or  hair-like  curved  cir- 
rus clouds  represented  in  the  outer  front  side  of  Fig.  269. 
If  these  are  seen  strongly  developed  in  any  quarter  of  the 
sky  it  is  usually  true  that  a  more  or  less  strongly  developed 
low  area  exists  in  that  direction. 

If  these  appearances  first  develop  to  the  east  of  a  north 
and  south  line  the  first  probability  is  that  this  storm  will 
not  reach  the  observer  because  it  is  already  past  and  trav- 
eling away  from  rather  than  toward  the  place. 

On  the  other  hand  if  the  cirrus  clouds  show  themselves 
•well  developed  to  the  west  of  a  north  and  south  line,  and 
especially  if  between  the  southwest  and  northwest,  then  a 
storm  center  is  located  where  its  future  course  may  bring 
it  over  the  locality. 

736.  Change  in  Wind  Direction. — If  a  storm  is  approach- 
ing from  the  westward  in  the  direction  of  the  cirrus  clouds 
these  will  advance  and  in  a  few  hours  will  overspread  the 
sky,  the  wind  will  decrease  and  finally  shift  to  a  direction 
which  will  indicate  the  approach  of  the  storm,  and  more 
definitely  the  direction  of  the  low  area  from  the  observer. 

737.  Direction   of  the   Storm   Center  Indicated   by  the 
Wind. — When  a  storm  has  advanced  far  enough  to  give 
definite  direction  to  the  wind  it  is  then  possible  to  judge 
from  this  the  location  of  the  storm  center. 

Standing  with  the  back  to  the  wind  and  extending  the 
right  arm  directly  in  front,  and  the  left  arm  at  right  angles 
to  this,  the  storm  center  is  usually  in  a  direction  somewhere 
between  the  two  hands;  this  will  be  clearly  seen  from  a 
study  of  Fig.  269  and  also  of  Fig.  268. 

It  will  sometimes  happen  that  winds  blowing  outward 
from  a  HIGH,  or  region  of  heavy  pressure  which  has 
passed  to  the  eastward,  may  be  mistaken  for  those  due  to 
an  approaching  storm,  because  they  are  easterly,  but  the 


580  Principles  of  Weather  Forecasting. 

character  of  the  sky  and  the  weather,  with  experience,  will 
usually  serve  to  distinguish  these  anticyclonic  winds  from 
those  belonging  to  the  cyclone  or  storm  proper. 

738.  Discovering  the  Course  the  Storm  Is  Traveling. — 
After  having  observed  the  existence  and  direction  of  a 
storm  center  it  is  important  to  know  whether  it  will  pass 
to  the  north  or  south  of  the  locality  or  whether  it  will  move 
directly  across  it.     This  can  be  foretold  by  the  changes  in 
the  direction  of  the  wind.     Referring  again  to  Fig.  269 
it  will  be  observed  that  if  the  storm  center  comes  directly 
toward  the  observer  the  direction  of  the  wind  will  hold 
steady  in  the  S.  E.  until  after  the  storm  has  passed,  when 
it  will  shift  abruptly  to  the  N.  W.,  as  indicated  by  the  ar- 
rows laid  on  the  axis  of  the  storm  track.     If,  however,  the 
storm  center  is  passing  considerably  to  the  north  of  the  ob- 
server the  winds  will  shift  toward  the  south,  finally  becom- 
ing S.  W.     But  if  the  low  area  is  passing  to  the  south  of 
the  observer  then  the  winds  will  shift  around  by  the  north, 
becoming  finally  !N".  W.  and  then  W. 

If  the  winds  hold  steady,  or  if  they  shift  to  the  north,  a 
general  rain  or  snow  may  be  expected,  unless  the  storm 
center  is  too  distant,  but  if  it  is  shifting  toward  the  south, 
showers,  rather  than  widespread  precipitation,  may  be  an- 
ticipated. After  watching  the  progress  of  storms  during 
two  or  three  months,  comparing  them  with  the  daily 
weather  maps,  one  becomes  able  to  recognize  with  much 
certainty  the  approach  of  all  well  marked  storms  and  to 
forecast  their  course  and  the  character  of  the  weather  12  to 
24  hours  in  advance.  Mistakes  will  occur,  just  as  they  do 
with  the  Weather  Bureau  expert  having  a  much  wider 
knowledge  before  him,  but  with  a  little  experience  the 
judgment  becomes  much  more  reliable  than  would  at  first 
be  expected. 

739.  Temperature  Changes  Connected  with  Storms Dur- 
ing the  colder  portions  of  the  year  the  temperature  changes, 
which  are  associated  with  the  progress  of  a  storm  across 


Forecasting  of  Weather  Changes.  581 

the  country,  are  often  very  marked.  The  general  rule  is 
that  with  the  approach  of  a  storm  the  temperature  rises 
above  the  normal  for  the  place  and  season,  if  it  is  the  cold 
part  of  the  year,  but  after  the  storra  passes  the  temperature 
falls  below  the  average. 

The  rise  in  temperature  is  due  to  three  causes:  (1)  The 
warming  of  the  air  by  the  heat  due  to  the  condensation  of 
moisture;  (2)  the  checking  of  radiation  by  the  moisture 
in  the  air ;  ( 3 )  the  importation  of  warmer  air  from  farther 
south  under  the  influence  of  the  storm  center. 

It  was  shown  in  (41)  and  (42)  that  the  formation  of  a 
pound  of  water  at  212°  from  a  pound  of  steam  at  212°  is 
associated  with  the  development  of  966  heat  units,  and  the 
freezing  of  a  pound  of  water  is  also  associated  with  the  ap- 
pearance of  142  heat  units.  When,  therefore,  a  pound  of 
snow  forms  in  the  air  from  a  pound  of  water  vapor  there 
is  imparted  to  the  air  in  which  this  occurs 

966  +  142  =  1108  heat  units 

and  if  snow  enough  falls  to  represent  an  inch  of  rain  the 
heat  produced  in  the  air  is  at  the  rate  of  about 

(jo  4. 
1, 108  X  ^  =  5761-6  heat  units 

UB 

per  square  foot  of  the  surface  upon  which  the  snow  falls. 
The  warming  of  the  atmosphere  when  it  snows  heavily 
must  be  very  considerable  and  this  is  why  it  is  seldom  more 
than  a  few  degrees  below  freezing  when  a  heavy  snow  is  in 
progress. 

The  low  temperature  following  a  storm  is  due  to  three 
chief  causes :  (1)  The  rapid  loss  of  heat  by  radiation  from 
the  ground  under  the  clear  sky ;  (2)  the  descent  of  cold  air 
from  high  altitudes;  and  (3)  the  importation  of  colder  air 
from  farther  north  under  the  influence  of  the  storm  center. 

If  reference  is  made  to  Fig.  268,  it  will  be  seen  that  the 
southeast  quadrant  has  a  mean  temperature  of  59°  F., 
while  the  northwest  quadrant  has  a  mean  temperature  of 
37 


582  Principles  of  Weather  Forecasting. 

only  17°  F.,  42°  colder.  In  the  northwest  HIGH  there 
is  a  temperature  of  — 10°  F.,  while  to  the  east  of  the 
LOW,  above  60°,  or  a  difference  of  70°  F.,  and  while  a 
part  of  this  difference  is  due  to  difference  of  latitude,  most 
of  it  is  due  to  the  effect  of  the  storm. 

740.  Barometric  Changes  Connected  with  Storms. — Dur- 
ing the  progress  of  a  storm  across  a  given  station  the  bar- 
ometer falls  more  or  less  gradually  until  the  center  has 
reached  the  place  and  then  it  begins  to  rise,  and  may  con- 
tinue to  do  so  until  a  pressure  greater  than  is  normal  has 
been  attained.     The  changes  of  the  barometer,  therefore, 
become  indices  of  the  approach,  progress  and  passage  of  a 
storm,    and    so,  too,  in    a  less    degree,  may    temperature 
changes  also,  during  the  winter.     If  the  barometer  falls 
faster  than  usual,  if  the  wind  velocity  increases  rapidly 
and  rapid  changes  in  the  wind  direction  occur,  the  indica- 
tions are  either  that  the  storm  center  is  approaching  at  a 
high  rate  of  speed  or  that  its  diameter  is  small  and  hence 
that  it  is  likely  to  arrive  sooner  after  indications  have  de- 
veloped. 

741.  Cold  Waves. — Cold  waves  in  the  United  States  are 
usually  the  result  of  a  strongly  developed  storm  which  has 
traversed  somewhat  slowly  the  southern  and  eastern  states. 
When  these  conditions  prevail  a  HIGH  area  with  clear 
sky  and  descending  cold  air  from  above  forms  over  Mani- 
toba, or  the  northern  boundary  of  the  United  States,  and 
the  strongly  developed  LOW  area,  traveling  slowly,  sets 
this  body  of  cold  air  in  motion  toward  it,  which  often  at- 
tains a  velocity  of  25  to  40  miles  per  hour.     Under  these 
conditions  intense  cold  is  rapidly  transported  southward 
and  eastward  with  the  speed  of  an  express  train,  and  occa- 
sionally temperatures  even  below  zero  are  transported  as 
far  south  as  northern  Alabama. 

Besides  the  extremely  cold  waves  just  referred  to  there 
are  others  more  common,  which  are  due  principally  to  the 
first  two  causes  named,  and  are  usually  coincident  with  the 


Cold  Waves. 


583 


HIGH  areas,  following  them  in  their  course  across  the 
country. 

742.  Forecasting     Warm     and     Cold     Weather. Since 

strongly  developed  storms  tend  to  draw  the  air  into  them- 
selves across  long  distances,  it  is  clear  that  when  they  pass 
to  the  south  during  the  cold  months  of  the  year  cold  waves 
are  likely  .to  follow  their  passage.     On  the  other  hand,  if 
the  low  area  has  passed  to  the  north  it  can  only  bring  air 
from  the  south  northward,  importing  but  little  cold  with 
it.     To  ,be  able  to  forecast  the  path  of  a  storm  then  is  also 
to  be  able  to  forecast  the  temperature  changes  which  are 
likely  to  follow. 

743.  Long  Warm  and  Dry  Periods. — It  frequently  hap- 
pens that  a  series  of  storms  follow  along  a  single  track,  one 
after  another  for  several  weeks  together,  and  Fig.  270  rep- 


FIG.  270. — Chart  showing  conditions  which  determine  dry  weather  in  the 
eastern  United  States. 


resents  one  of  these  sets  of  conditions.     During  the  month 
of  October,  1895?  all  but  four  of  the  fifteen  low  areas  re- 


584: 


Principles  of  Weather  Forecasting. 


corded  by  the  Weather  Bureau,  moved  along  axes  within 
the  northern  belt  marked  "axis  of  low  areas." 

It  is  clear  that  so  long  as  such  conditions  as  these  pre- 
vail but  little  rain  could  fall  in  the  United  States,  and  all 
the  northern  portion  must  have  unusually  warm  weather. 
The  weather  must  be  clear  and  dry  because  along  the  axis 
of  high  pressure  the  air  is  descending  from  the  higher  al- 
titudes where  it  is  already  dry,  and  in  descending  must 
become  still  dryer  because  of  increasing  temperature  due 
to  compression.  As  this  is  the  air  which  must  be  drawn 
toward  the  low  areas  on  either  side  of  the  axis  it  could  con- 
tribute but  little  moisture  for  rainfall  in  either  system  of 
lows,  and  the  map  shows  that  but  little  fell. 


FIG.  271.— Path  of  the   West  Indian   Hurricane   of   Sept.   1-11,   1900. 

So  long  as  a  high  pressure  occupies  the  Gulf  and  At- 
lantic states,  this  effectually  shuts  off  the  moist  gulf  and 
ocean  air  and  forces  the  storm  centers  to  maintain  a  high 
northerly  course.  Then,  too,  as  long  as  storms  pursue  a 


Tropical  Cyclone. 


585 


course  off  the  Atlantic  border  they  also  must  shut  off  the 
moisture  from  the  northern  states  and  tend  to  maintain 
warm,  dry  weather  there. 

Whether  in  this  case  the  two  systems  of  low  areas  were 
the  cause  of  the  belt  of  high  pressure  which  prevailed,  or 
whether  the  high  pressure  belt  simply  marks  the  place 
where,  for  some  reason,  the  upper  air  from  the  general 
wind  system  was  falling  to  the  earth,  the  outcome,  so  far 
as  the  weather  is  concerned,  must  be  essentially  the  same. 

744.  Tropical  Cyclones. — During  the  latter  part  of  Aug- 
ust, September  and  the  fore  part  of  October  it  frequently 
happens  that  storms  of  unusual  magnitude,  intensity  and 
destructiveness  originate  in  the  north  tropical  zone  of  trade 
winds,  somewhere  in  or  to  the  east  of  the  Carribean  Is- 
lands and,  after  traveling  westward  with  the  prevailing 


FIG.  272.— Path  of  West  Indian  Hurricane  of  Aug.  7-14,  1899. 

winds  of  that  zone,  they  finally  make  their  way  northward 
across  the  tropical  calm  belt  and  break  into  the  zone  of 
southwest  winds,  making  their  way  northward  and  east 
ward,  as  represented  by  the  two  storm  tracks  in  Figs.  271 
and  272,  the  former  being  the  storm  which  produced  the 
terrible  destruction  of  life  and  property  at  Galveston  on 


586  Principles  of  Weather  Forecasting. 

September  8,  1900,  when  more  than  5,000  human  lives 
and  $20,000,000  of  property  were  lost. 

The  severe  cold  winds  which  are  designated  as  the 
"Northers"  of  Texas  owe  their  origin  to  storm  centers  of 
unusual  intensity  off  the  Gulf  coast,  which  set  large  bodies 
of  air  in  motion  from  the  northward,  drawing  it  into  them- 
selves as  they  pass  along  to  the  southward  and  eastward. 


THUNDER    STORMS,    HAIL,    STORMS    AND    TORNADOES. 

Associated  with  the  ordinary  storms  which  have  been 
described  in  a  preceding  section  there  are  others  much 
more  local  in  their  character,  shorter  in  duration,  but  often 
more  violent  in  wind  movement  and  precipitation.  These 
are  thunder  storms,  hail  storms  and  tornadoes. 

745.  Relation  of  Tornadoes  and  Thunder  Showers  to  Ordi- 
nary Storms. — Careful  study  of  the  time  of  occurrence  and 
distribution  of  these  storms  has  shown  that  they  are  almost 
always  associated  in  a  definite  way  with  some  cyclonic 
wind  movement,  and  that  they  usually  originate  to  the 
southeast,  south  or  west  of  south  of  a  storm  center,  in  the 
region  designated  by  the  cumulus  clouds  in  the  diagram, 
Fig.  269. 

746.  Tornadoes. — Tornadoes  are  whirling  winds  of  ex- 
treme violence  which  last  but  a  short  time,  progressing  al- 
most always  from  the  southwest  toward  the  northeast,  often 
at  the  rate  of  a  mile  per  minute,  sweeping  a  belt  40  to  80 
rods  wide  and  several  miles  long.     Sometimes  the  width 
of  the  zone  of  destructive  winds  may  reach  a  full  mile. 
At  the  center  of  the  tornado  the  moisture  is  swept  together 
by  the  revolving  winds  into  a  dark  funnel-shaped  cloud, 
where  the  velocity  of  the  whirling  air  may  be  so  great  that 
few  structures  can  withstand  the  enormous  pressure  they 
develop. 


Tornadoes  and  Thunder  Storms 


58T 


x  5v' 


\    x 


\X    VV 

\Xv-Si 


x^c 

2    N  -  • v  -  • 

°x  x  /^\^^^^^^^:>r^A^-::-^:':'^ 

y^  -  V"  ^^^^^^^'''^'^•it^ 


^^^ummmii 

^Q  ,  ^  >~-SMS^SlSS 

>^/^faifeteliiiii 


FIG.  273. — Diagram  showing  the  origin  of  tornadoes  and  thunder  storms. 


588  Principles  of  Weather  Forecasting. 

747.  Schools  of  Tornadoes — When  the  conditions  are  ex- 
tremely favorable  for  the  formation  of  tornadoes  they  often 
appear  in  schools,  originating  one  after  another  or  simul- 
taneously, as  the  main  storm  center  progresses  across  the 
country,  and  Fig.  273  shows  how  these  local  but  violent 
storms  are  related  to  a  storm  center  and  how  many  may 
develop  in  the  southeast  quadrant  as  it  travels  along.     In 
this  figure  the  short,  heavy  straight  lines  to  the  southeast 
of  the  center  represent  the  paths  of  tornadoes  which  devel- 
oped during  its  course. 

748.  Distribution  of  Thunder  Showers. — Thunder  show- 
ers, like  tornadoes,  originate  in  the  great  majority  of  cases 
to  the  southeast  and  south  of  a  well  developed  storm  center 
and  often  large  numbers  of  them,  scattered  over  consider- 
able areas,  form  as  the  storm  progresses,  much  as  is  the 
case  with  tornadoes,  and  Fig.  274  is  a  diagram  showing 
the  advance  of  the  front  along  which  thunder  showers  orig- 
inated in  a  storm  of  early  May,  1892,  as  recorded  in  the 
Monthly  Weather  Review  of  that  month,  p.  138. 

On  May  3  a  long  low  area  had  advanced  from  the  south 
and  west  and  at  8  P.  M.  its  lowest  portion  was  central 
north  of  Lake  Huron.  The  front  of  the  thunder  shower 
line  had  reached  the  east  end  of  Lake  Erie  at  2  P.  M.  of 
the  same  date  and  showers  were  in  progress  along  the  line 
marked  2  P.  M.  in  Fig.  274.  As  the  storm  center  ad- 
vanced the  thunder-shower-front  also  moved  forward  and 
swept  across  the  state,  as  shown  by  the  curves  on  the  dia- 
gram, reaching  Long  Island  at  2  A.  M.  on  the  morning  of 
May  4th,  the  front  thus  progressing  from  20  to  30  miles 
per  hour. 

749.  Conditions  Tinder  Which  Thunder  Showers  and  Tor- 
nadoes Originate. — In  the  diagram  of  Fig.  273  are  repre- 
sented the  wind  directions  and  temperature  relations  which 
exist  when  conditions  are  favorable  for  the  formation  of 
both  of  these  classes  of  storms.     There  is  a  region  of  warm 
moist  southerly  winds  to  the  south  and  east  of  the  low  area 


Formation  of  Thunder  Storms. 


589 


and  another  region  of  decidedly  colder  winds  blowing 
from  the  west  and  north  of  west ;  and  it  is  along  the  meet- 
ing of  these  two  systems  of  winds  that  thunder  showers 
tend  specially  to  form,  and  in  advance  of  it  that  the  tor- 
nadoes have  their  birth. 


FIG.  274.— Diagram    showing    the    progressive    development    of    thunder 

storms. 

750.  Formation  of  Tornadoes. — The  most  satisfactory  ex- 
planation of  the  formation  of  tornadoes  is  represented  in 
the  lower  portion  of  Fig.  273,  which  is  a  cross-section  of 
the  lower  portion  of  the  atmosphere  at  right  angles  to  the 
line  dividing  the  two  systems  of  winds  shown  in  the  upper 
portion  of  the  same  diagram. 

It  is  supposed  that,  under  these  conditions,  the  cold  west 
and  northwest  winds  at  times  over-run  the  moist  warm  and 
lighter  southerly  stratum,  thus  producing  a  condition  of 
unstable  equilibrium.  When  such  conditions  have  been 
developed  the  warm  air,  at  some  point,  is  supposed  to 
break  up  through  the  over-running  colder  layer,  as  shown 
in  the  lower  right-hand  corner  of  the  diagram,  and  in  do- 


590 


Principles  of  Weather  Forecasting. 


ing  so  is  thrown  into  a  rapidly  whirling  movement  in  the 
same  manner  that  water  runs  into  whirls  in  discharging 
through  the  bottom  of  a  wash-bowl.  When  the  volumes  of 
air  which  must  change  places  are  large  and  the  stratum 
of  cold  air  deep,  there  comes  ultimately  to  be  developed 
an  enormous  rotary  velocity  which  gives  to  the  air  an  ex- 
tremely destructive  power. 


V 


FIG.  275. — Diagram  of  the  path  of  a  tornado. 

751.  Explosive  Violence  of  Tornadoes. — At  the  center  of 
a  tornado  cloud  the  rapidly  whirling  motion  reduces  the 
air  pressure  at  the  center  of  the  funnel  so  much  as  to  pro- 
duce a  high  vacuum,  and  when  a  building  lies  in  the  path 
of  the  funnel  the  vacuum  surrounds  it  so  suddenly  that 
often  the  great  pressure  of  air  within  the  building  will 
throw  the  walls  outward  or  lift  the  roof  off  before  the  air 
has  time  to  escape  into  the  vacuum  formed  by  the  tornado. 


Formation  of  Tornadoes. 


591 


752.  Unsteady  Action  of  Tornadoes. — A  tornado  seldom 
displays  a  uniformly  destructive  power  and  oftentimes 
the  point  of  the  funnel  fails  to  reach  the  ground  and  con- 
siderable gaps  are  passed  in  the  path  where  little  damage  is 
done.  This  unsteady  action  is  often  due  to  the  slowing 
up  of  the  rotary  motion  in  the  cloud  due  to  the  great  fric- 
tion developed  at  the  ground.  After  withdrawing  to  the 
upper  air  the  speed  increases  sufficiently  to  allow  the  fun- 
nel to  grow  to  the  surface  again  and  resume  the  destructive 
work. 

When  the  funnel  reaches  the  surface  it  does  not  always 
describe  a  straight  path  along  the  ground,  but  tends  to 
cross  and  recross  the  main  axis  of  movement. 


FIG.   276.— Diagram  showing  the  rotary  movement  of  winds  in  a  tornado. 

753.  Character  of  the  Tornado  Path. — It  is  usually  true 
that  the  path  of  a  destructive  tornado  is  not  symmetrical, 
one  side  being  wider  than  the  other,  as  represented  in  Fig. 
275,  where  it  will  be  seen  that  the  northwest  side  is  nar- 
rower than  the  southeast  side.  Not  only  is  the  zone  of  de- 
structive winds  wider  on  the  south  side  but  that  of  the 
sensible  winds  is  also.  On  account  of  this  character  of 
the  tornado  track  it  is  clear  that  if  one  has  an  occasion  to 
escape  from  an  ordinary  tornado,  the  shortest  path  would 


592  Principles  of  Weather  Forecasting. 

lie  to  the  northwest,  at  right  angles  to  the  line  of  progress. 
The  evidences  of  a  rotary  motion  of  the  air  in  a  tornado 
are  abundant  and  conclusive,  and  in  Fig.  276  are  repre- 
sented some  of  these. 

754.  Formation  of  Thunder  Showers. — Thunder  showers 
appear  to  have  an  origin  similar  to  that  of  tornadoes,  but 
evidently  occur  where  there  is  less  air  to  change  places,  and 
probably  also  where  the  depth  of  the  overlying  stratum  is 
less.  Indeed,  it  appears  very  often,  if  not  generally,  true 
that  a  volume  of  cold  heavy  air  has  dropped  directly  to 
the  ground  and  is  moving  bodily  against  the  warmer  moist 
air,  which  it  is  forcing  upward,  as  represented  in  the  lower 
left-hand  corner  of  Fig.  273.  The  rapidly  ascending 
warm  moist  air  is  cooled  by  expansion  and  by  mixing  with 
the  cold  air,  thus  giving  rise  to  the  heavy  precipitation  so 
often  observed. 

The  rolling  movement  shown  in  the  diagram  is  often 
violent  enough  and  involves  so  great  a  hight  in  the  at- 
mosphere, that  often  raindrops  are  carried  round  and 
round  until  they  become  very  large  before  they  are  able  to 
fall.  If  the  vertical  circulation  reaches  above  the  zone 
of  freezing  temperature  the  raindrops  freeze,  forming  hail. 
These  hailstones,  in  the  most  violent  storms,  are  often 
carried  around  with  such  force  and  so  many  times  that  they 
become  very  large  before  they  are  able  to  overcome,  by 
their  weight,  the  velocity  of  the  air;  and  fall  to  the  ground. 


INDEX, 


Air,  movements  through  soil,  125 ;  elas- 
ticity of,  8 ;  moisture  absorbed  from 
by  soils,  177  ;  need  for  in  soil,  204 ; 
volume  changes  with  temperature,  207  ; 
volume  of  in  soil,  208  :  composition  of 
respired,  350 ;  micro-organisms  In, 
3t>2  ;  amount  respired,  35<i,  354,  355  ; 
degree  of  impurity  permissible,  354 ; 
sunnly  for  stables,  355 ;  introduction 
Into  stables,  355,  356,  357,  362,  363, 
364 ;  exclusion  of  from  silos,  394 ; 
warming  of,  560,  581 ;  pressure  per 
BQ.  ft.,  532  ;  see  atmosphere. 

Alfalfa,  developing  mulch  for,  193. 

Alkali,  amount  limiting  plant  growth, 
93  :  in  Yellowstone  Park,  93 ;  in  Al- 
geria, 93 ;  white,  93 ;  black,  93 ; 
amount  influenced  by  tillage,  98. 

Alkali  lands,  correction  for,  95 ;  drain- 
age remedy  for,  98. 

Ammonia,  occurrence  in  soil,  83 ;  conver- 
sion into  nitric  acid.  86  ;  in  rain  water, 
86 ;  removed  from  lungs,  351 ;  in  at- 
mosphere and  rain,  86,  557. 

Aniline,  divisibility  of,  9. 

Animals,  as  motors,  487 ;  as  soil  pro- 
ducers, 64. 

Animal  temperature,  regulation  of,  33 ; 
normal,  343. 

Anticyclone,  561,  571,  572. 

Ants,  in  formation  of  soil,  67  ;  drainage 
allows  deeper  penetration,  290. 

Architecture,   rural,  329. 

Argon,  amount  of  in  atmosphere,  557. 

Arid  soils,  50,  73  to  75. 

Artesian  wells,  general  flow  of  water 
supplying,  270 ;  conditions  for  forma- 
tion. 277. 

Atmosphere,  554  ;  influence  on  tempera- 
ture, 23,  557 ;  source  of  plant  food. 
554,  558  ;  relation  to  earth,  554  ;  rela- 
tion to  life,  5.*>5  :  depth  of,  556  :  com- 
position of,  556  ;  materials  suspended 
In,  557  :  functions  of  ingredients,  557  ; 
pressure,  559  :  temperature  of,  560  ; 
movements  of,  561 ;  general  circula- 
tion, 562,  564. 

Atoms,  7. 


B 

Babbitt  metal,  515. 

Baker,  J.  O.,  drainage  system  of  Ron- 
toul,  III.,  309. 

Balloon  frame,  340. 

Barley,  nitrogen  used  by,  62  ;  alkali  salts 
limiting  growth  of,  94  :  water  used  by, 
143 :  root  development  of,  150,  153 ; 
germination  temperature.  212. 

Barn  frames,  forms  of,  339;  plank,  340; 
balloon,  340;  round,  341. 

Barns,  frames  of,  339,  340,  341  ;  best 
temperature  for,  344 ;  relation  of 
hight  to  capacity,  367 :  separate  or 
consolidated,  370 ;  avoiding  posts  in, 
374  ;  stable  floors,  374  ;  watering  in, 
388  ;  unloading  hay  in,  391 ;  ventila- 
tion of.  350. 

Barometric  pressure,  559,  568,  569 : 
changes  influence'  soil'  ventilation, 
208  ;  causes  change  of  level  of  water 
in  wells,  173 ;  of  rate  of  discharge 
from  springs,  273 ;  of  rate  of  dis- 
charge from  tiled  drains,  271 ;  changes 
of  in  storms,  575,  582. 

Basement  stables,  ventilation  of,  355, 
356,  364  ;  may  be  sanitary,  364. 

Beams,  strength  of,  331,  332,  334  :  com- 
puting loads  for,  336 ;  table  of  safe 
loads,  338. 

Beans,  nitrogen  used  by,  82 ;  germina- 
tion temperature,  212. 

Bedding,  use  of,  376. 

Beef  fat,  fuel  value  of,  33. 

Belting,  543  ;  action  of,  543 ;  efficiency. 
543 ;  computing  size,  544 ;  care  of. 
544  ;  management  of.  545  ;  lacing  of, 
545 :  computing  length  of,  546. 

Berthelot,  on  soil  nitrogen,  89. 

Tlidwell,  stall,  385. 

Boiler,  508 :  construction  of.  509 :  care 
of,  512 ;  cleaning,  512:  firlne.  51:{; 
foaming,  513  ;  low  water  in,  514  ;  ex- 
plosion of,  514 :  soft  plug,  51 1 ; 
water  for,  515,  517. 

Boiler  scale,  512,   517. 

Box  stall,  ventilation  of,  387. 

Braces,  uses  of,  338. 

Brick,  walls  of,  347,  402  ;  vitrified,  403. 


594 


Index. 


Brick-lined  silos,  construction    of,    403 ; 

lining  for,  406. 
Brick     silos,     construction      of,      400 ; 

strengthening  walls  of,  401,  402. 
Brown-Sequard,  on  respiration,  352. 
Building  paper,  for  walls,  348 ;  for  silos, 

41o. 


Calcium,  essential  plant  food,  69 ;  func- 
tion of,  71. 
Calm  belts,  .jUo  to  »<'.'.>. 

Capillarity,  modified  l>y  dissolved  salts, 
106  ;  principle  of,  .'57. 

Capillary  capacity,  innxinnim  of  soils  for 
water,  182  ;  of  sands  for  water,  134  ; 
influenced  by  distance  above  standing 
water,  134. 

Capillary  rise,  in  glnss  tubes.  37.  Ifil  :  of 
water  in  soils,  103 ;  in  sandy  loam, 
165  :  in  clay  loam.  10.> ;  in  sand.  107  ; 
in  wet  soil,  1G8  ;  in  dry  soil  168:  in- 
fluenced by  rain.  170,  190 ;  by  farm 
yard  manure.  172,  by  soil  mulches, 
173.  by  firming  the  soil,  174,  by  sub- 
soiling.  199. 

Carbon  dioxide,    mode     of    escane     from 
lungs,  6  ;  number  of  molecules  in  one 
gram,  10  :  removed  by  soil  ventilation 
206  :  causes  flocculation  of  clay,  210 
inexpired   air,   350 :    heavier   than   air 
361 :  danger  from  in  filling  silos,  427 
source  of  carbon   in  plants.   554  :  per 
cent,    of    in    atmosphere,    557 ;    influ- 
ence of  on  temperature,  558. 

Cattle,  normal  temperature  of.  344  ;  ties 
for.  384  :  tying  for  feeding,  387. 

Cement,  kinds  of,  379 ;  for  silo  walls 
398,  402,  406,  407. 

Cement  floors,  379 :  condensation  of 
moisture  on,  351 ;  temperature  of, 
375  ;  construction  of,  379 :  materials 
for.  380 :  ratio  of  ingredients  for, 
381  :  laying.  382  :  cost,  383  ;  for  cel- 
lar or  creamery.  383;  for  silos,  410. 

Chamberiin,  cause  of  glacial  periods, 
559. 

Cheese  curing  rooms,  masonry  walls  for, 
347  :  construction  of.  347.  348. 

Chemical  changes  produced  by  ether 
waves,  24 :  influence  of  on  soil  tem- 
perature. 219 ;  source  of  power  in  en- 
gir.ps.  486. 

Chemical   nature  of  soils,   69,   74,   75. 

Chlorine,  essential  to  fertile  soil,  69. 

Chloronlivll.  requires  iron  In  soil,  70: 
cells.  143. 

Clay,  difference  between  puddled,  and 
soil.  233 :  shrinkage  checks  when 
drained,  290. 

Clay  soil,  aluminum  silicate  In,  49  ;  com- 
pared with  sandy.  71,  74,  75,  with 
others,  73  :  amount  of  plant  food  per 
acre  foot,  80 :  flocculation  by  carbonic 
acid,  210.  290. 


Clover,  plant  food  contained  In  79 ; 
sowing  seed  before  frost  is  out,  193 ; 
germination  temperature,  213 ;  water 
used  by,  141 ;  extent  of  root  develop- 
ment, 150,  156. 

Coal,  fuel  value  of,  502. 

Coal  tar,  use  on  floors,  377 ;  use  on  silo 
linings,  407. 

Coathupe,  amount  of  air  respired,  353. 

Cohesion,  6. 

Cold,  nature  of,  25. 

Cold  waves,  582. 

Colin,  amount  of  air  breathed,  354. 

Collars,  for  tile  drains,  292. 

Color,  influence  on  soil  temperature, 
217  ;  waves  of,  23. 

Conservation  of  energy,  19. 

Contour  maps,  of  surface,  256 ;  of 
ground  water,  257,  259. 

Corn,  variation  of  soluble  salts  in  soil 
under  with  season,  96  ;  water  used  by. 
141;  root  development  of,  150,  152. 
154,  157  ;  early  fitting  of  ground  for. 
185;  danger  in  late  cultivation,  189. 
190;  best  time  to  cultivate,  192;  hill- 
ing 194 ;  plowing  for  in  fall,  252  : 
grinding  by  windmill,  536. 

Coulter,  effect  of  on  draft  of  plow,  243 

Cover  crops,  object  of,  183  ;  danger  of, 
201. 

Cows,  normal  temperature  of,  344  : 
stable  temperature  for,  344 ;  amount 
of  air  respired,  354  ;  supply  of  air  for. 
355 ;  cubic  feet  of  space  for,  357 ; 
ties  for,  384. 

Crops,  amount  of  water  required  by, 
139:  proportion  of  soil  water  avai- 
lable to,  135 ;  soils  which  yield  moist- 
ure most  completely,  136. 

Cultivation  after  heavy  rains,  190  • 
depth  of  to  save  moisture,  191 ;  fre- 
quency of,  187 :  frequency  vary  with 
season,  191 ;  influence  of  frequency  on 
mulches,  189;  influence  of  depth  on 
effectiveness  of  soil  mulches  189  • 
ridged  and  flat,  194 ;  too  great  fre- 
quency undesirable,  189. 
Cultivators,  for  intertillage,  226- 
spring  tooth,  227;  with  wiae  shovels' 
227;  with  rigid  teeth,  228;  teeth  of 
adjustable,  228 ;  disk  form,  229  •  for 
surface  cultivation,  229 ;  garden  types, 

Culverts,  479. 

Cyclone,  562,  570,  571,  572,  576;  trop- 
ical, 585. 

Cylinder  of  pump,  in  well.  546,  551 ; 
of  steam  engine,  518,  520;  water 
jacket  for  in  gasoline  engine,  524  ;  o* 
double  acting  pump,  550. 

D. 

Darcy's  law,  262,  269. 

Darwfn    formation  of  soil,  65 ;  soil  con- 


Index. 


595 


Denltrifleatlon,  process  of,  In  dry  earth 
closet,  90 ;  ill  sewage  water,  90 ;  in 
water-logged  soils.  90.  205 :  in  marsh 
soil,  90. 

Deodorizing  milk,  16. 
Deodorizer,  17. 

Deserts,  relation  to  wind  zones,  565. 
DeVries,     alkali     salts,     limiting     plan 

growth,  93. 

Diffusion,  principles  of,  40 ;  influence  o 

temperature  on,  40  ;  slow  rate  in  soi 

40  ;  in  plant  feeding,  46 ;  in  soil  ven 

tilation,   207. 

Disease,   caused  by  lack  of    ventilation 

352. 

Disk  harrow,  234 :  use  in  early  spring 
to  develop  mulch,  185  ;  to  fit  seed  bee 
234. 

Distributing  cart,  469,  470. 
Ditch  digging,  322  ;  shaping  and  eradin 
bottom,  322  ;  placing  tile  in,  324  ;  fil 
ing,   328. 

Dog,  normal  temperature,  344. 
Doors,  construction  of  for  silos,  396 
399,  403,  411,  421,  423 ;  strengthen 
ing  wall  between,  399,  402,  410,  423 
Draft  on  macadam  road,  18 ;  of  plow 
241,  243 ;  influence  of  soil  moisture 
on  draft  of  plows,  244 ;  line  of  in 
plow,  246 ;  principles  of,  428 ;  rela 
tion  to  grade,  430 ;  of  wagons,  434 
436,  490  ;  relation  of  width  of  tire  to 
436 ;  of  size  of  wheel,  437 ;  of  dis 
tribution  of  load.  438 ;  of  line 
draft,  440,  492,  497 ;  of  rigidity  of 
carriage,  442  ;  of  speed,  491 ;  of  hours 
work  per  day,  492 ;  of  weight 
horse,  493  ;  of  distribution  of  weight 
in  the  horse,  494  ;  of  strength  of  hock 
muscle,  494  ;  of  width  of  hock,  495  ; 
line  of  in  sweep  power,  502. 
Drainage,  remedy  for  alkali  lands,  98 ; 
rate  of,  determined  by  pore  space,  115  ; 
may  increase  available  soil  moisture, 
139,  288  ;  influence  on  soil  ventilation, 
210,  290 ;  influence  on  soil  tempera- 
ture, 222,  228 ;  necessity  for,  286  ;  in- 
creases root  room,  287  ;  conditions  re- 
quiring, 287 :  interception  of  surface, 
306;  of  basins  without  outlets,  307; 
of  flat  areas,  309  ;  intercepting  under- 
flow, 307  ;  practice  of,  311 ;  tools  for, 
312,  321 ;  determining  levels  for  312  ; 
of  roads  445,  448,  449  ;  water-breaks, 
449. 

Drains,  fluctuations  in  rate  of  flow  from. 
270 ;  barometric  changes  in  rate  of 
flow  from.  271 ;  temperature  changes 
in  rate  of  flow  from.  271 :  kinds  of, 
290:  depth  of.  292:  distance  be- 
tween, 296  ;  surface  of  ground  watei 
between,  297 :  rate  of  change  of 
ground  water  between,  297  :  gradient 
for,  298 :  uniform  fall  for  important, 
298  :  outlet  for,  302,  303  :  connection 
of  sub-main  with  main,  303  :  joining 
lateraf  with  main,  303 ;  obstructions 


to,  303  ;  laying  out  systems  of,  304  ; 
construction  of  surface,  30(J  ;  levoMin? 
for,  312  ;  locating  mains  and  laterals, 
315 ;  determining  grade  and  depth, 
317  ;  changes  in  grade.  310. 

Drown,   cow  stall,   385. 

Dry  earth  closets,  denitriflcation  in,  90. 

Dust  in  soil  formation.  ti4  :  micro-organ- 
isms, in  of  houses  and  stables,  352  ; 
avoiding  in  concrete,  380 ;  of  atmos- 
phere, 557,  558. 

E. 

Ebermayer,  best  temperature  for  growth, 
212  ;  observed  soil  temperatures,  314. 

Eel  grass,  63. 

Elbows,  resistance  to  flow  of  water, 
550. 

Elliott,  C.  G.,  size  of  tile,  301,  302. 

Energy,  19  ;  conservation  of,  19  ;  trans- 
formation of,  20  ;  solar,  20,  22  :  unita 
of,  27 ;  amount  required  to  melt  ice, 
30  ;  to  evaporate  water,  31. 

Engine.  518  ;  steam,  502  ;  gasoline,  522  ; 
see  steam  and  gasoline. 

Erdmann,  function  of  potash,  70. 

Ether  waves,  21 ;  velocity  of,  22  ;  kinds 
of,  23  ;  transparency  to,  24  :  produce 
evaporation  and  chemical  changes,  24. 

Evaporation,  24,  30 :  heat  required  for, 
30 ;  rate  of  influenced  by  dissolved 
salts,  106 ;  influence  of  on  soil  tem- 
perature, 32,  220. 

Evener,  kinds,  496  ;  principles  of,  497 ; 
giving  one  horse  the  advantage,  498 ; 
more  than  two  horse,  499. 


Fallow  ground,   nitric   acid   In,    84 ;   ni- 
trates in,  103  ;  loss  of  nitrates  from, 

104. 
Farm  buildings,   frames,   340 ;   means  of 

controlling  temperature,  346  ;  lighting 

of,  348  :  ventilation  of,  350. 
'arm  machinery,  538. 
Farm  motors,   kinds,   486  ;  tread   power, 

499  ;  sweep  power,  501  :  steam  engine, 

502  ;  gasoline   engine,    522  ;    windmill, 

5oT. 
Fattening  animals,  best  temperature  for. 

344. 

'eeding,  of  odor  producing  foods,  15. 
errel.  world  system  of  winds.  563. 
ertility,    of   soils    in    arid    regions,    50 ; 

conditions  essential  to.  69. 
"•ertilizers,  diffusion  of  through  soil.  11; 

influence    of,   on   amount    of   nitrogen 

removed  from  soil,  82. 
'ield  soils,  permeability  of  to  air,   127 ; 

weight  of  dry,  per  cu.  ft.,  127  ;  heavy 

and  light,  128. 
issures  in  rock,  53. 
lavors,  in  dairy  products.  14  :  how  they 

are    absorbed,    14 ;     removal    of.     Iti"; 

time  to  feed  odor-producing  foods,  1§. 


596 


Index. 


Floors,  stable,  374 ;  temperature  of, 
375 ;  wood,  377  ;  stone,  378 ;  cement, 
379  ;  comparative  cost,  383  ;  manure 
drop,  388. 

Foaming,  in  boiler,  513. 

Foot-pound  18,  27 ;  equivalent  in  beat 
units,  28. 

Foot-ton,  18,  27. 

Frank,  symbiosis,  88. 

Frear,  Dr.,  soil  temperatures,  214. 

Freezing,  with  ice  and  salt,  30. 

Friction,  538 ;  kinds,  538 ;  between  sol- 
ids, 539;  rolling,  540;  of  fluids,  540; 
lubricants,  541 ;  influence  of  grit  on, 
542. 

Furrows,  dead  and  back,  49. 

G 

Gage,   cocks,   510 ;  glass,  510 ;  pressure, 

Galvanized   iron,   silo   lining,   414. 

Gardens,  early  plowing  of  to  save  moist- 
ure, 185  ;  floating,  205  ;  cultivators  for, 
230. 

Gasoline  engine.  522  :  parts,  523 ;  work- 
ing cycle,  523:  cooling  of  parts,  524; 
types  of,  524 ;  construction,  525, — • 
cylinder,  525, — pumping  mechanism, 
525, — governor,  526. — -valve  mechan- 
ism, 528  ;  igniting  charge,  529 ;  lubri- 
cation, 529  ;  gasoline  for,  530. 

Gasoline,  for  engine,  530. 

Germination,  interfered  with  by  green 
manure,  201 :  retarded  by  too  early 
seeding,  201 ;  oxygen  needed  for,  204 ; 
temperatures  for,  213 ;  rate  of  in- 
fluenced by  soil  temperature,  214 ;  of 
weed  seeds,  225. 

Glacial  soils.  57. 

Governor.  521,  526. 

Grade,  428 ;  effect  on  draft,  429 ;  steep- 
est admissible,  430 ;  conditions  which 
determine,  433. 

Grain,  ratio  of  to  straw,  80 ;  harrowing 
after  up.  192,  224  ;  rolling  after  up, 
192,  224 :  fitting  seed  bed  with  disk 
harrow,  235. 

Grapes,  affected  by  alkalies,  93. 

Gravel,  457  ;  for  road  surface,  456  ;  char- 
acter, 458,  459 ;  altering  texture,  458. 

Gravel  roads,  459. 

Green  manures,  danger  from,  201 ;  plow- 
ing under,  253. 

Grinding,  by  wind  mill,  531,  536. 

Ground  water,  movements  of,  255 ;  con- 
tours of  surface  of.  257,  259  ;  changes 
in  level  of,  260  ;  elevation  of  through 
percolation,  260  ;  changes  with  season, 
260  :  general  movement  of  across  wide 
areas.  270  ;  fluctuations  in  rate  of  flow 
of,  270 ;  changes  in  rate  of  flow 
due  to  barometric  changes,  271 : 
diurnal  changes  in  rate  of  flow 
of,  271,  272 ;  rise  of  away  from 
drainage  outlets.  203.  285 :  observed 


surface  In  tile-drained  field,  297  :  rate 
of  change  in  level  between  tile  drains, 
297. 

Guard  cells,  143 ;   action  of,   144 ;   loss 
of  water  through,  145. 


Haberlandt,  temperature  of  germination, 
214. 

Hail,  formation  of,  524. 

Harrow,  spike-tooth,  to  save  moisture, 
185 ;  disk  harrow  to  save  moisture, 
185;  for  small  grain  after  it  is  up, 
192 ;  for  corn  and  potatoes  after  they 
are  up,  192  ;  tilting,  225  ;  use  in  kill- 
ing weeds,  224,  225  ;  spring  tooth,  233  ; 
smoothing  type,  236 ;  should  follow 
roller,  237. 

Harrowing,  influence  of  on  soil  ventila- 
tion. 210  ;  after  plowing.  252. 

Hay,  arrangements  for  unloading,  391. 

Heat,  25 ;  mechanical  equivalent.  28 ; 
specific,  29 :  latent.  29.  5N1  :  froin 
green  and  wet  woods,  35  ;  control  of  in 
animals,  343 ;  normal  for  animals, 
343  ;  construction  to  prevent  change, 
345 ;  produced  by  muscular  action, 
488 ;  loss  from  engines  506. 

Heat  unit,  28 ;  number  of  consumed  In 
melting  and  in  evaporation,  30.  220  ; 
number  of,  In  one  pound  of  beef  fat, 
and  one  pound  of  milk,  33;  value  of 
wood  in,  35 ;  value  of  coal  In,  502. 

Hedges,  as  wind  breaks,  202. 

Hellriegel,  on  symbiosis,  87 ;  effect  of 
temperature  on  rate  of  germination, 
214. 

Hens,  air  breathed  by,  354,  355. 

Herbst,  respiration,  353. 

Hilgard,  soil  analyses,  71,  74,  75 ; 
humus  of  arid  climates,  76 ;  alkali 
salts  limiting  plant  growth.  93 ;  on 
hygroscopic  moisture,  177,  179. 

Hock  joint,  495. 

Hoops,  for  silos,  399,  422. 

Horse,  normal  temperature  of,  344  ;  air 
respired  by,  354 ;  supply  of  air  for, 
355  :  as  a  motor,  487  :  generation  of 
energy  by,  489, — expended  in  hauling 
loads,  490, — in  plowing,  491 ;  trac- 
tion of  491 ;  principles  of  draft  of, 
493,  494,  495,  496 ;  equalizers  for, 
496,  499 ;  in  tread  power.  500. 

Horse  power,  27  ;  measure  of  solar  en- 
ergy, 22 ;  equivalent  of,  consumed  In 
melting  ice  and  in  evaporating  water, 
30 :  of  horses,  490, — in  hauling  loads, 
490, — in  plowing,  491 ;  in  tread 
power,  500  :  of  engine.  530 ;  trans- 
mission of  by  belts,  544. 

Hot  box,  542. 

Hot  tube,  529. 

Humus.  76  ;  of  arid  and  humid  climates, 
76  :  loss  from  and  need  for  in  sandy 
soils,  206 ;  on  sandy  roads,  457. 


Index. 


597 


Humus  soil,  formation  of,  55,  61 ;  plant 
food  per  acre  foot,  80. 

Hurricane,  West  Indian,  584,  585. 

Hutchinson,  respiration,  353. 

Hydraulic  ram,  552. 

Hydrogen,  rate  of  molecular  vibration,  9  ; 
size  of  molecules,  10. 

Hygroscopic  moisture,  175 ;  movements 
'of,  175 ;  relation  of  to  diameter  of 
soil  grains,  176  ;  amount  absorbed  by 
soil,  177  ;  influence  of  temperature  on, 
179. 


Ice,  melting  of,  29 ;  In  soil  formation, 
57 ;  for  cooling  milk,  34 ;  melting 
for  water,  35. 

Illinois  soils,  nitrogen  in,  82. 

Injector,  516. 

Infiltration  pipes,  lowering  ground 
water,  295. 

Ions,  48. 

Iron,  essential  to  fertile  soil,  69 ;  func- 
tion of,  70. 

Irrigation,  by  windmill,  531,  536. 

Isobars,  568,  569,  575,  584,  585. 


Jaffa,  humus  of  arid  climates,  76. 
January,   winds  of  world,  567,  568. 
Jeffery,   denitrification,   90. 
Jointer,  attachment  for  plow,  249  ;  use  in 

plowing  under  green  manure,  253. 
Joule,  heat  unit,  28. 
July,  winds  of  the  world,  567,  569. 


Kelvin,     Lord,     size    of    molecules,     9 ; 

solar  energy,  22. 
Kosswitch.  symbiosis,  88. 
Kuhn,  Julius,  connection  of  lateral  with 

main    drain,    303. 
Kunkle,  safety  valve,  512. 


Lacing,  belts,  545. 

Lakes,    in   formation  of  humus   soil,  62. 

Laurent,    symbiosis,    88. 

Lawes,  Sir  J.  B.,  Rothamstead  experi- 
ments, 81. 

Lawes  and  Gilbert,  nitrogen  in  soil,  82. 

Leaching,  effect  of  in  soil  formation,  77  ; 
a  correction  for  alkali  lands,  95. 

Leveling  a  field,  methods  of,  314  :  con- 
tour map.  315 :  locating  mains  and 
laterals,  315 ;  laying  out  drains, 
317 ;  determining  grade  and  depth, 
318  ;  changing  grade,  319. 

Levers,   of   arm,   489 ;   mechanical   prin- 
ciple of,  498. 
38 


Lighting,  farm  buildings.  348  ;  efficiency 

of  windows,  349. 
Lime,  function    of    in    plant    life,    71 ; 

amount  removed  by  crops,  79 ;  amount 

in   soil,   80. 
Limestone,    formation   of   soil    from,    52. 

78  ;   source  of  water  supply,  276  ;   for 

road  metal,  466,  469  ;  for  binding,  466. 
Line  of  draft,  in  plow,  246  ;  in  wagons. 

440,  441. 
Lining,   for  silos,   413 ;    brick,   402,   406, 

403 ;     galvanized     iron,     414 ;     4-inch 

flooring,  414 ;     half-inch     boards     and 

paper,   415 ;   painting,   418. 
Loam,  effectiveness  of  as  mulches,  186. 
Loess,  64,   73,   74,   75  ;   amount  of  plant 

food  in  acre  foot,  80. 
Los    Angeles    Water    Company,    diagram 

of  flume,  295. 
Low  area,  494,  507  ;  course  of,  505  :  re-i 

latlon  of  to  cold  waves,  514';  to  warm 

dry  periods,  515. 
Lubricator,  Swift,  521. 
Lubricants,  541 ;     reduction     of  friction 
by,  541 :  selection  of,  541  ;  for  gaso- 
line engines,  529. 

M 

Macadam,  Engineer,  462,  467 ;  roads, 
462  ;  road-bed  for,  463  ;  rock  for,  46'4, 
466 ;  without  binding  material,  467 ; 
thickness  of,  473  ;  rolling  of,  473  ;  for 
stable  floor,  378  ;  for  barn  yard,  379. 

Magnesia,  as  plant  food,  69  ;  function  of, 
71 ;  amount  removed  by  crops.  7J> ; 
amount  in  an  acre  foot  of  soil,  80. 

Mairs,  T.  J.,  draft  of  wagons,  437. 

Man,  oxygen  consumed,  influenced  by 
temperature,  345 ;  air  respired  by,  353, 
354. 

Mangers,  388. 

Manitoba  soils,  nitrogen  in,  82. 

Manure,  effect  of  capillarity,  172 ;  as 
mulch  for  meadows,  193  ;  green.  201 ; 
ventilation  hastens  fermentation,  206; 
plowing  under,  253. 

Manure  drop,  388. 

Maple,  fuel  value  of,  35. 

Maps,  contour  of  ground  water,  257, 
259  ;  of  surface,  256. 

Marsh  soils,  formation  of,  62 ;  analyses 
of,  73,  74,  75  :  as  mulches,  186 ;  tem- 
perature of,  220. 

Masonry  walls,  relation  to  temperature, 
347  ;  for  silos,  397,  400.  405,  409,  422. 

Maxwell,  size  of  molecules.  10. 

Melon,  temperature  for  germination,  212. 

Melting  of  ice,  30,  35. 

Micro-organisms,  in  soil,  50 :  convert 
humus  into  nitric  acid,  76 ;  soil  al- 
gae, 88 ;  nitrifying  germs,  89 ;  de- 
nitrifying germs,  90 ;  require  air,  205 : 
in  air  of  unventilated  buildings.  352, 
dangers  from,  353 ;  in  the  atmosphere, 
557. 


598 


.  Index. 


•Milk,  odors  and  flavors  in,  14  ;  deodoriz- 
ing of,  16;  cooling  of,  17,  34;  value 

:     of,  in  neat  units,  33. 

Mixed  herbage,  nitrogen  used  by,  82. 

Molecules,    6 ;    composed    of    atoms,    7 ; 

.'  not  in  contact,  8;  movements  of,  8, 
13 ;  diffusion  of,  8 ;  relation  to  elastic- 
ity,  8 ;  velocities  of,  9 ;  number  of  per 

.  gram,  10,  11 ;  size  of,  9 ;  relation  of 
to  steam  pressure,  19 ;  movements  in 
evaporation,  24;  dissociation  of  in  so- 
lution, 48. 

Monsoons,  570. 

Morin  Gen.,  draft  of  wagons,  443 ;  fric- 
tion, 540. 

Motors,  farm,  486. 

Mulches,  effectiveness  of,  in  marsh  soil, 
186 ;  sandy  loam,  186 ;  clay  loam, 
186  ;  character  influenced  by  frequency 
of  cultivation,  187 ;  depth  of.  189, 

f  191 ;  depth  and  frequency  of  stirring 
should  vary  with  season,  191 ;  de- 
veloped by  rolling,  193 :  other  than 

•  soil,   193 ;  for  alfalfa  fields,  193  ;  for 
meadows.  193. 

Miintz.  denitriflcation,  90. 

Muscles,  as  motors,  .487  ;  temperature  of 

in  action,  488 ;  power  of,  488  ;  of  hock, 

.494. 
Mustard,    temperature    of    germinatioa. 

212 

N 

Nitrates,    seasonal    changes   under   corn, 

•  96 :   in  cultivated     and     uncultivated 
ground,  100 ;  relation  of  to  total  sol- 
uble salts,   101 ;   closeness  of  removal 
of  by  plants,  101 ;  in  fallow  and  crop- 

•  ped  ground  compared.    103.  105 ;    loss 
of    during    wintej,    104 ;    development 
influenced  by.  cultivation,  105 ;  by  late 

.  ,fall  plowing,  182  ;  loss  of  lessened  by 
cover  crops,  183  ;  developed  by  early 
tillage.  185  ;  air  required  for  develop- 

•  ment   206;  temperature  for  formation, 
212,  215. 

Nitric  acid,  amount  of  in  soils,  84 ;  in 
.  fallow  ground^.  84  ;  action  of  ozone  and 

'peroxide  of  hydrogen  in  formation  of, 

,  86 ;  formation,  of,  89  :  formed  by  niter 

'germs,   89;    in'  atmosphere,   557. 

Nitric  nitrogen,  in  soil,  84 ;  limiting 
amount  for  corn  and  oats,  102, 

Nitrification,  process  of,  89 ;  tempera- 
ture for,  212. 

Niter  germs,  forming  nitric  acid,  89; 
temperature  for  growth  of,  212. 

Nitrogen, .  essential  to  plant  life,  69; 
form .  of  used  by  plants,  70 ;  from 
humus,  76 ;  amount  removed  by  crops, 
79,  82 ;  amount  stored  in  soils,  82 ; 
forms  of  occurrence  in  soil,  82  ;  dis- 
tribution of  in  soil.  83 ;  source  of  in 

'  Boil,  85  ;  accumulated  by  '  symbiosis, 
87 ;  increased  in  soil,  by  ventilation, 
206  ;  of  plants  derived  from  air.  554  ; 
amount  In  air,  556 ;  functions  of,  558. 


Nobbe,  function  of  potash,  70. 
Nobert,  ruling  of  glass  by,  9. 
Nollet,  Abb6,  41. 
Northers,  of  Texas,  586. 


Oak  value  of  one  pound  of  in  heat 
units,  35. 

Oats,  water  used  by,  141 ;  nitric  nitrogen 
limiting  growth,  102  ;  extent  of  root 
development,  150,  155. 

Odors,  8,  13;  in  dairy  products,  14; 
accumulation  of  in  dairy  products,  14  ; 
removal  of,  16. 

Oemler,  specific  heat  of  soils,  215. 

Orchards,  late  tillage  of  to  conserve 
moisture,  182;  early  plowing  for,  185. 

Osmosis,  phenomena  of,  41;  principles 
of,  42;  measurement  of  pressure,  43; 
in  plant  feeding.  46. 

Osmotic  pressure,  42;  influence  of  tem- 
perature on,  46;  increased  by  dissocia- 
tion of  salts,  48. 

Oxalic  acid,  action  in  plant  growth,  70, 
71.  . 

Ox-bows.  .55,  57,  62. 

Oxygen,  absorption  of  in  breathing,  6 ; 
rate  of  molecular  motion,  9 ;  size  of 
molecules,  10 ;  essential  to  germina- 
tion, 204  :  uses  in  soil.  204  ;  essential 
to  plant  breathing,  204  ;  amount  con- 
sumed by  man  varies  with  tempera- 
ture, 345 ;  demand  for  necessitates 
ventilation,  350  ;  amount  in  air,  557 ; 
functions  of,  557. 

Ozone  action  of  in  forming  nitric  acid, 
86  ;  in  atmosphere,  557. 


Paper,  function  of  in  walls,  348 ;  es- 
sential qualities.  348 :  for  ventilators, 
364  ;  for  silos,  400,  407,  415. 

Peas,  temperature  for  germination,  212. 

Peat,  formation1  of,  62. 

Percolation,  rate  influenced  by  pore 
space,  115;  of  teoil  moisture,  158; 
rate  of  through  sand  and  soil,  159 ; 
through  dry .  sojl.  160 :  rate  of  in- 
creased by  sub-soiling,  199 :  influence 
of  on  soil  ventilation.  209 ;  rise  of 
ground  water  due  to,'  260. 

Pfeffer.  osmotic  pressure.  44,  4fi. 

Peroxide  of  hydrogen,  action  of  in  form- 
ing nitric  acid,  86. 

Perspiration     controls     body     tempera- 

•    ture,  33. 

Phosphoric  acid,  in  soil,  74,  78,  80; 
amoiint  removed  by  crops.  79. 

Phosphorus  essential  to  plant  life,  69; 
function  of,  70. 

Pillars;' strength  of,  330;  bearings  for, 
330. 

Piston,  of  steam  engine.  519 :  of  gasoline 
engine,  525  ;  size  of  for  pumps,  547. 


Index. 


599 


Pit  silos,  423. 

Plank   frame,   340. 

Flanker,  use  of,  236. 

Plant  food,  essential  constituents,  69 ; 
functions  of,  70 ;  proportion  of  total 
soil,  78  ;  amount  removed  by  crops,  79  ; 
in  an  acre-foot  of  soil,  79,  81 ;  con- 
served by  early  seeding,  201 ;  Impor- 
tance of  temperature  in  development 
of,  212 ;  loss  of  through  weeds,  224  ; 
manner  of  supply  to  plants,  46 ;  de- 
rived from  the  air,  554. 

Plants,  growth  of  limited  by  soluble 
salts,  93  :  breathing  of,  142  ;  respira- 
tory organs  of,  142. 

Plastering,  silo  walls,  398,  402,  403,  406, 
407. 

Plow,  238 ;  as  a  tool  to  develop  texture, 
238;  forms  of,  239;  for  sod,  240, 
241  ;  soil  and  function  determine 
form,  240 ;  for  pulverizing  soil,  242  ; 
for  mellow  soil,  242 ;  draft  of,  243, 
244.  245 ;  draft  influenced  by  soil 
moisture,  244  ;  line  of  draft  in,  246  ; 
scouring  of,  247  ;  care  of,  247  ;  jointer 
attachment  for,  249 ;  sub-soil  form, 
250. 

Plowing,  to  conserve  soil  moisture,  181, 
182,  IS'! ;  early  for  corn  and  potatoes, 
185 ;  may  puddle  soils,  239 :  to  cor- 
rect texture.  239;  depth  of,  250;  con 
dition  of  soil  for,  251 ;  treatment  ef 
ground  after,  252 ;  for  corn  in  the 
fall,  252  :  sod,  252  ;  covering  manure, 
253;  green  manure,  253:  early  fall, 
254  ;  horse  power  required  for,  491. 

Poisons,  12. 

Pore  space,  of  soils,  111,  233  ;  maximum 
and  minimum  for  spherical  grains, 
109,  111.  114  :  influence  on  water  ca- 
pacity, 114  ;  of  different  kinds  of  soil, 
114 ;  iiiJluence  of  suu-uivision  of  on 
rate  of  percolation,  115  ;  method  of  de- 
termination, 115  ;  maximum  in  soils, 
116 ;  shape  of,  163.  164  ;  necessary  for 
roots,  233 ;  in  sands  and  gravels, 
256 ;  in  soil  and  clay,  257 :  unoccupied 
in  drained  sands,  261 ;  influence  of  on 
capacity  of  wells,  276 ;  for  materials 
for  concrete,  381. 

Posts,  strength  of,  330 ;  avoiding  use  of 
in  barns,  374. 

Potash,  essential  to  plant  growth,  69 ; 
function  of,  70 ;  amount  removed  by 
crops,  79 ;  amount  in  soil,  80 ;  in 
wheat  crop,  81. 

Potatoes,  amount  of  water  used  by,  141 ; 
early   plowing  for,    185 ;   best  time  to 
cultivate,    192 ;    ridged    and    flat    cul- 
tivation for,   194. 
Precipitation,  rise  of  ground  water  due 

to,  260. 

Pressure,  relation  of  to  flow  of  water, 
262.  268 :  influence  of  on  capacity  of 
wells.  279:  of  gases,  40;  osmotic,  42; 
relation  of  to  volume  of  gases,  41 ; 


measurement  of  osmotic,  43  ;  of  silage, 
394 ;  of  atmosphere,  559 ;  of  steam, 
504  ;  gage,  511 ;  on  piston  in  pumping, 
547,  548. 

Priming,  in  engine,  506. 
Pulley,  relation  to  belts,  545. 
1'urnp,   capacity   of   on    sand   point   com- 
pared   with    open    suction     pipe,    282 ; 
cross-head,  575 ;  in     gasoline     engine, 
525  ;  suction,  546  ;  size  of  piston,  547  ; 
rate    of    discharge,    548 ;    relation    ct 
size    to    discharge    pipe,    548 ;    double- 
acting,  550  ;  place  for  cylinder,  551. 
Pumping,  by  windmill,  531,  535  ;  rate  of. 
536 ;   power  for   influenced   by   size  of 
discharge  pipe,  548. 
Pusey,  draft  of  plows,  243 

Q 

Quincke,  distance  over  which  cohesive 
attraction  becomes  sensible,  37. 

It 

Rain,  bad  effect  of  on  animals,  33 ; 
evaporation  of,  33  ;  ammonia  and  ni- 
tric acid  in,  86 ;  cultivation  after, 
190;  influence  of  9n  soil  temperature, 
219 ;  effect  of  on  rise  of  ground  water, 
261. 

Rainfall,  relation  to  storm  center,  575; 
conditions  unfavorable  for,  584. 

Ram,  hydraulic,  552. 

Respiration,  products  of,  350,  351 ; 
amount  of  air  breathed,  353. 

Richthoffen,  formation  of  loess,  64. 

Rivers,  formation  of  soil  by,  54,  55,  56, 
57. 

Roads.  428 ;  grade  of,  428 ;  effect  of 
grade  on  draft,  428 ;  steepest  grade 
admissible,  430  ;  conditions  modifying 
grade.  433 ;  draft  on  different  kinds, 
436.  437,  443  ;  establishing  grade,  444  ; 
drainage  of,  445, — relation  of  water  to, 
446, — depth  of,  446, — place  for  drains, 
447,,— fall  of  drains,  447, — outlet  of 
drains,  448, — size  of  tile,  448, — sur- 
face, 448  ;  slope,  449  ;  water-breaks, 
449  ;  texture  of  road  metal,  450, — size 
of  material,  451,  shape  of  material, 
451. — cleanness.  452  :  earth,  452,  477. 
— forming  road-bed,  452,  455, — util- 
izing old  road-bed,  455 ;  on'  grav- 
elly loam,  455 :  on  clay  soil,  455 ; 
on  sandy  soil,  456 ;  use  of  straw,  saw- 
dust and  tan  bark,  457 ;  gravel  for, 
457  ;  in  swampy  places.  460  ;  stone, 
461 ;  ancient  types,  461 ;  macadam, 
462, — construction.  462,  463, — road 
metal  for,  464,  465,  466.  467, ,  468, 
469, — spreading  rock,  470. — thickness 
of  layers,  473, — rolling,  473,  474,  475 ; 
roller,  kind,  475 ;  rock  crusher,  459, 
475 :  rock  screens,  459,  477 ;  com- 
bined roads,  477  :  Telford  foundation, 
478  ;  culverts,  479  ;  maintenance,  480. 


600 


Index. 


Headmaster,  481. 

Roberts,  stall,  385. 

Rocks,  formation  of  soil  from,  50 ;  In- 
fluence of  fissures  on  soil  formation, 
53  ;  composition  of  compared  with  soil 
77 ;  composition  of,  78 ;  flow  of  water 
through  262  ;  kinds  for  roads,  464. 

Rock  crushers,  459,  475. 

Roller,  uses  of,  236 ;  weight  of  for  farm 
use,    237 ;    types    of,    237 ;    danger   in 
uses  of,   237 ;   should   be   followed   by 
harrow,    237 ;    may    strengthen    capil- 
lary rise  of  soil   moisture,  174 ;   as  a 
tool    for    producing    mulch,    192 ;    in- 
'  fluence    of    on    soil  temperature.  221 ; 
'for  roads,  473,  475,  484, — size,  473. 

Rolling,  grain  after  up,  192 ;  influence 
of  on  soil  ventilation,  210 ;  influence 
of  on  soil  temperature,  221 ;  influence 
of  on  capillary  rise  of  water,  174  ;  of 
roads,  474  . 

Roman  roads,  461.  478  :  roads,  474. 

Root  hairs,  structure  of,  147 ;  relation  of 
to  soil  grains,  147,  148 ;  method  of 
gathering  water,  147 :  conditions  for 
Improved  by  proper  tilth,  233. 

Root  pressure,  influence  of  soil  tempera- 
ture on,  215. 

Roots,  functions  of,  145 ;  absorbing  por- 
tion of,  146  ;  structure  of  root  hairs, 
147  ;  advance  of  through  soil,  148  ;  ex- 
tent of  development  of  in  corn,  150, 
151,  152,  154  ;  in  grain,  150,  153,  155  ; 
total  system,  154,  155.  156,  157: 
near  surface  late  in  season,  189 ; 
Influence  of  on  soil  ventilation,  210 ; 
room  for  increased  by  drainage,  287 ; 
obstruct  tile  drains,  303. 

Rothamstead,  experiments  at,  81 ;  nitro- 
gen in  soil  at,  82. 

Round  barn,  frame.  341 ;  consolidated 
type,  371  ;  handling  hay  in,  391. 

Rowland,  heat  unit,  28. 

Ruberoid  roofing,  for  ventilators,  364 ; 
for  silo  doors,  411,  423. 

Russia,  nitrogen  In  soils  of,  82. 


Salt  used  with  Ice  as  freezing  mixture, 
30  ;  solution  of,  7. 

Sal-soda,  for  boiler  scale,  517. 

Sanborn,  J.  W..  draft  of  plows,  243. 

Sand,  specific  heat  of.  29,  32,  216  ;  flow 
of  water  through,  123  ;  rate  of  percola- 
tion through,  159 ;  water  reservoir, 
255  ;  law  of  dow  of  water  through,  262  ; 
method  of  measuring  flow  of  water 
throneh.  264.  267  :  relation  of  pressure 
to  flow  through,  266  ;  observed  rates  of 
flow  through,  268  ;  sandstone,  capacity 
for  water,  255  ;  rate  of  Uow  of  wate'r 
through,  268 :  apparatus  for  measur- 
ing flow  of  water  through.  269 ;  as 
source  of  water  for  wells,  276. 


Sandy  soil,  compared  with  clay,  71,  74, 
75 ;  amount  of  plant  food  in,  80 ; 
wind  breaks  to  protect,  202 ;  rapid 
decomposition  of  humus  in,  206. 

Sand  strainers,  uses,  280 ;  capacity  of 
compared  with  open  suction,  281. 

Scale,  in  boilers.  517. 

Schlosing,  denitrification,  90. 

Schlosing,  Jr.,  symbiosis,  88. 

Schmidt,  C.,  nitrogen  in  soils,  82. 

Schroeder,  function  of  potash,  70. 

Scouring  of  plows,  247. 

Screen  rock,  451,  459.  477. 

Seed"  bed.  thorough  nreparation  for.  222. 

Seeds,  absorption  of  moisture  by,  6.  60  ; 
require  magnesia,  71 ;  germination, 
213,  225. 

Seepage,  growth  of  streams  due  to,  258. 

Sheep,  bad  effect  of  cold  rains  on,  33, 
amount  of  air  breathed,  354. 

Sheeting,  silos,  405,  412,  414. 

Showers,  thunder,  586  ;  relation  to  low 
areas,  576,  588  :  formation  of,  592. 

Shubler,  weight  of  soils,  128. 

Silage,  conditions  for  preserving,  394 ; 
lateral  pressure.  394  ;  loss  of  in  stave 
silo,  420 ;  weight  per  cu.  ft.,  424 : 
proper  feeding  area,  425 ;  generation 
of  carbon  dioxide  in,  427. 

Silos,  relation  of  depth  to  capacity.  367  : 
importance  of  depth,  394  :  rigidity  of 
walls,  394  :  depth  of  in  ground,  395  ; 
construction  against  free/ing,  396 ; 
stone,  397;  laying  wall,  397.  402; 
plastering,  398  ;  doors,  396,  399,  403, 
411  423 ;  strengthening  walls,  399, 
401.  402.  410 :  brick ;  400 ;  brick- 
lined,  403;  sill,  405,  410  :  setting^ stud- 
ding, 405.  411 :  sheeting,  405,  412, 
414;  siding,  406.  412;  lining.  403, 
40fi.  413:  round  plastered.  407:  wood. 
409 ;  foundation,  400,  405,  409 ;  ce- 
menting bottom,  382.  410  :  plate,  413  ; 
roof,  417  ;  ventilation.  417  :  decay  of, 
417;  painting  lining,  418:  stave,  418; 
hoops  for,  422  ;  pit  silo,  423  ;  capacity 
of.  424  :  feeding  area,  425  ;  danger  in 
filling,  427. 

Silt  basin,  construction  and  use,  299. 

Slichter,  C.  S.,  formula  for  computing 
effective  diameter  of  soil  grains,  121 ; 
formula  for  flow  of  water  through 
soil,  262  ;  computed  capacity  of  wells, 
280. 

Smell,   sense,   delicacy  of,   13. 

Smith,  Angus,  denitrification,  90. 

Smith,  C.  S.,  strength  of  pillars,  329. 

Snow,  latent  heat  of,  34 ;  melting  for 
washing,  35. 

Snow    storm,    chilling   effect    from    heat 

lost  in  melting,  34. 

Sod  plow,  form,  241,  draft  of,  243.  244 ; 
dralt  compared  with  stubble,  244. 

Sodium  nitrate,  number  of  molecules  per 

gram,   11. 
Soft   plug,   514. 


Index. 


601 


Soil,  temperature  low  when  wet,  29 ; 
cooled  by  evaporation.  32  ;  nature  of. 
49  ;  compared  with  subsoils,  49,  72,  74, 
75 ;  clayey  types,  49,  71,  74,  75 ;  uses 
of,  50  ;  micro-organisms  in,  50  ;  forma- 
tion of,  51 ;  rock  texture  in  formation, 
51  ;  conversion  of  limestone  into,  52  ; 
influence  of  rock  fissures  on  soil  forma- 
tion, 53  ;  removal  of,  53  ;  produced  by 
running  water,  54,  originating  through 
glaciers,  57,  58,  59,  60,  formation  of 
humus  type,  61,  62,  63 ;  formed  by 
wind  action,  63  ;  loess,  64  ;  produced 
by  animals,  64 ;  convection,  65,  ac- 
tion of  earth  worms,  66,  67  :  chemical 
nature  of,  69,  71 ;  chemical  composi- 
tion, 69,  71,  74,  75,  78,  81;  constitu- 
ents of  essential  to  fertility,  69  ;  com- 
parison of  kinds,  72,  74,  75  ;  of  arid 
and  humid  regions,  73,  76 ;  chemical 
nature  compared  with  parent  rock,  77  ; 
plant  food  removed  from  by  crops,  79, 
plant  food  in  acre  foot,  79  ;  nitrogen 
in,  82 ;  forms  in  which  nitrogen  oc- 
curs in,  83  ;  distribution  of  nitrogen  In, 
83 ;  amount  of  nitric  acid  iu,  84 : 
sources  of  nitrogen  in,  85 ;  soluble 
salts  in  field,  92  ;  physical  nature  of, 
108 ;  texture  of,  108 ;  number  of 
grains  per  cubic  inch,  109 ;  pore 
space  of,  111 ;  surface  of  per  gram, 
118,  per  pound,  118,  per  cubic  foot, 
124  ;  movement  of  air  through.  125 ; 
heavy  and  light,  128 ;  weight  per 
cubic  foot,  127 ;  capacity  of  for  water, 
131,  134  ;  kinds  yielding  moisture  to 
crops  most  completely,  136 ;  advance 
of  roots  through,  148  ;  rate  of  percola- 
tion from,  159,  160;  capillary  rise  of 
water  in,  163 ;  mulches,  185 : 
changes  in  temperature  of,  207 ;  im- 
portance of  right  temperature  of,  212  ; 
observed  temperatures,  213 ;  specific 
heat  of.  215.  21  fi:  temperature  In 
fluenced  by  color,  217,  by  texture,  218. 
by  topography,  218,  by  tillage,  219, 
by  chemical  changes,  219 ;  by  rain, 
219,  by  evaporation,  32.  212 ;  best 
condition  of  for  plowing,  251. 

Soil  grains,  number  per  cubic  inch, 
109, — per  gram,  118, — per  pound,  117  ; 
specific  gravity  of,  110  ;  effective  diam- 
eter, 121,  124  ;  method  of  determining 
effective  diameter,  121 :  computed  sur- 
face of,  124  ;  relation  of  water  capacity 
to,  124  ;  relation  of  root  hairs  to.  147  ; 
relation  of  diameter  of  to  flow,  266. 

Soil  kernels,  size,  110  :  relation  to  tex- 
ture, 231 ;  "destruction  of  In  puddled 
soil,  239  :  illustration  of,  231. 

Soil  moisture.  129 ;  movements  of  Influ- 
enced by  soluble  salts.  106 :  loss  of. 
lessened  by  soluble  salts,  107 ;  relation 
of  per  cent,  of  to  thickness  of  water 
film,  137 ;  amount  of,  affected  by 
jointed,  structure,  138;  amount  in-j 
creased  by  open  texture.  138 ;  amount  1 


available  Increased  by  drainage,  139, — 
by  subsoilmg,  200 ;  types  of  move- 
ment, 158;  percolation  of,  158;  grav- 
itational movements  of,  158 ;  capil- 
lary movements  of,  161 ;  observed 
hight  of  capillary  rise  of,  165, — influ- 
enced by  rain,  170,  190, — by  farm 
yard  manure,  172, — by  mulches,  173, — 
by  firming  the  soil,  174  ;  thermal 
movements  of,  175  ;  hygroscopic,  175 ; 
conserved  by  early  fall  plowing,  182, — 
early  spring  plowing,  183 ; — by  sub- 
soiling,  195, — by  early  seeding,  200, — • 
by  wind  breaks,  202 ;  possible  waste 
through  untimely  cultivation,-  189; 
movement  of,  affected  by  subsoiling, 
197  ;  danger  of  loss  of  through!  green 
manuring,  201 ;  loss  through  action 
of  weeds,  224  ;  Influence  of  on  draft  of 
plows,  244. 

Soil  mulches,  effectiveness  of,  185 ; 
method  of  demonstrating  influence  of, 
187. 

Soil  surface,  Influence  of,  on  chemi- 
cal analyses,  72 :  amount  per  gram, 
118, — per  pound,  118, — per  cubic  foot, 
124  ;  difficulty  of  determination,  119. 

Soil  temperature,  212  ;  importance  of  to 
life  forms,  212  ;  at  which  growth  be- 
gins, 212  ;  best  for  germination,  212 ; 
influence  of  on  rate  of  germination, 
214  ;  effect  of  on  root  pressure,  215 ; 
influence  of  color  on,  '217, — of  to- 
pography on,  218, — of  unevenness  of 
surface  on,  218,-— of  looseness  of  sur- 
face on,  219, — of  tillage  on,  219, — of 
physical  and  chemical  changes  on,  219, 
— ^i  rams  on,  219, — of  evaporation, 
220, — of  rolling  on,  221, — of  prepara- 
tion of  seed  bed  on,  222, — of  under 
draining  on,  222,  287  ;  means  for  con- 
trolling, 221. 

Soil-tube,  116. 

Soil  water,  viscosity  of  modified  by  salts, 
106 ;  proportion  of  available  to 
crops,  161 ;  internal  evaporation  of, 
179 ;  conservation  of,  181 ;  modes  of 
controlling,  181,  late  fall  plowing  to 
conserve,  181. 

Solar  energy,  20 ;  rate  of  transmission, 
22,  amount  of,  22. 

Soluble  salts,  amount  In  field  soils,  92 ; 
amount  of  limiting  plant  growth,  93, 
in  Yellowstone  Park,  93;  In  Algeria, 
93;  why  injurious  to  plants,  93  ^con- 
centration of  in  zones,  94  ;  origin  of, 
94;  removal  of  by  leaching,  95;  In 
marsh  soils,  95  ;  change  in  amount  of 
with  season,  98  ;  variation  of  with  dif- 
ferent crops,  99 ;  influence  of  on  move- 
ments of  soil  moisture,  106 :  modifica- 
tion of  surface  tension  by,  106  :  lessen 
the  loss  of  soil  moisture.  107  :  influence 
in  cementing  soil  granules.  233  ;  drain- 
age of  to  remove  excess,  286. 

Solution,  38 ;  Influence  of  temperature 
on,  39  ;  saturated.  39. 


602 


Index. 


Specific  gravity,  of  soil  grains,  110. 
Specific   heat,    29 ;   of   dry    soil,   215 :   o 
wet  soils,  216  :  of  water,  216  :  of  moor 
earth,  216 ;  of  humus,  216 ;  of  loam 
216  ;  of  clay,  216  ;  of  sand,  216  ;  chalk 
216. 

Springs,  fluctuations  In  rate  of  flow.  270 
Squash,  germination  temperature,   213. 
Stables,    temperature    for,    344 ;    ventila 
tion  of,  355  to  365  ;  floors  for,  374  to 
384. 

Stalls,  for  cows,  384  to  387. 
Stanchions,   384,   386,  388. 
Starch,  potassium  required  for  formation 

of.  70. 

Stave  silo,  418  to  423. 
Steam,    pressure   of.    504 :   dry   and   wet, 
504  ;  condensation  of,  506  ;  water  for, 
517 

Steam  engine,  502  •  principle  of  502  ;  ef- 
ficiency of,  503 ;  dry  and  wet  steam, 
504 :  priming,  505  to  508 :  relief 
cocks,  507 ;  boiler,  508 ;  construction, 
509,  518 ;  gage  cocks,  510 ;  gage 
glass,  510  ;  pressure  gage,  511 ;  safety 
valve,  511 ;  care  of  boiler,  512  ;  firing, 
513 ;  foaming.  513 ;  low  water  in, 
514  ;  water  for,  515 ;  fly-wheel,  522 ; 
governor,  521. 
Stone  roads,  401. 
Stone  silos,  397. 
Storm  center,  575. 
Storms,  570  ;  wind  directions  in,  570  to 
572 :  progressive  movements  of,  572 
to  574  ;  rate  of  travel,  574 ;  diameter 
of,  574 ;  duration  of,  575 ;  region  of 
precipitation,  575  ;  prediction  of,  578 
to  580 ;  temperature  changes  of,  580 ; 
barometric  changes  of,  582 ;  thunder 
and  hail,  586. 

Strength  of  materials,  329 ;  of  pillars, 
330 ;  tensile,  331 ;  transverse,  331  to 
336  :  breaking  constants,  336  ;  comput- 
ing breaking  loads,  336  ;  safe  quiescent 
center  loads.  337. 
Stress,  kinds,  329. 

Stubble  plow.  242  ;  draft  of,  243,  491. 
Studding,     use  in     balloon     barn  frame, 
341 ;  in  round  barn,  242  ;  in  silo,  405, 
411. 

Suction  pump,   546 :   double-acting.   550. 
Subsoils,  jointed   structure  in,    138 ;    in 
arid    regions.     50 ;     chemical  composi- 
tion. 74  :  differ  from  soils,  72  ;  should 
not  *">  turned  UD  by  plow.  251. 
Subsoiling  to  save  moisture,  195  ;  meth- 
od of  demonstrating  effect  of  on  soil 
moisture,    196 :    moisture     effects     of, 
198 :  how    water  capacity  is  Increased 
by.  198 ;  decreases  capillary  rise,  199 ; 
Influence  of  on   percolation,   199 :    in- 
creases per  cent,  of  available  moisture, 
200  ;  dangers  from,  200 ;  influence  of t 
on  soil  ventilation,  209  ;  plow  for,  250  ; 
ventilation.  209. 
Subsoil   plow,   250. 
Sugar,  osmotic  pressure,  45. 


Sulky  plow,  245. 

Sulphur,  essential  to  fertile  soil,  69 ; 
function  of,  70. 

Sulphuric  acid,  in  soils,  74,  80  :  removed 
by  crops,  79. 

Sun,  source  of  earth's  energy,  20. 

Surface  drainage,  where  needed,  306, 
309. 

Surface  drains,  construction  of,  306. 

Surface  tension.  36 :  overcome  in  evap- 
oration, 24  ;  in  solution,  38  :  modified 
by  dissolved  salts,  106 ;  effect  of  on 
soil  texture,  233. 

Sweep    power,    501. 

Swine,  normal  temperature  of,  344 ; 
amount  of  air  breathed,  354. 

Symbiosis,  source  of  soil  nitrogen,  87; 
need  of  soil  ventilation  for,  206. 


Tanks,    for   watering   stock,   389,    390. 

Telford,  road  construction,  462,  478. 

Temperature,  25  ;  expansion  due  to,  7 ; 
of  interplanitary  space,  23 ;  measure- 
ment of,  25 ;  for  cooling  milk,  34 ; 
regulation  of  in  animal  body,  33  ;  in- 
fluence of  hygroscopic  moisture  on, 
179;effect  of  changes  in  onsoil  ventila- 
tion, 207 ;  importance  of  right  for 
soil,  212  ;  of  water  in  wells,  284  :  see 
soil  temperature ;  control  of,  343, 
346 ;  normal  for  animals,  343 ;  for 
stables,  344,  345  ;  force  in  ventilation, 
359  ;  construction  for  control  of  345 
to  348,  367  ;  atmospheric,  560 :  influ- 
enced by  storms,  575,  580,  582,  583; 
effect  on  wind  power,  532  ;  of  muscles, 
488  ;  of  steam,  504. 

Terraces,  of  river  valleys,  55. 

Texture,  of  rock  in  soil  formation.  51 ;  of 
soil,  108,  231 ;  influence  on  loss  of 
soil  moisture,  183  ;  changed  in  sub- 
soiling,  199  :  influence  of  on  soil  tem- 
perature, 218 ;  modified  by  tillage, 

232  :  Importance  of,  233,  development 
of,    233 ;   difference   of   in   soil    and    in 
Potter's    clay,    233 ;    of    puddled    soil, 

233  :  developed  by  plow,  238 ;  effect  of 
after-treatment  on.   252  :   of  road  ma- 
terial, 450,  451,  456,  458.   459. 

Thermometer,  8,  26 ;  accuracy  of,  26 ; 
wet  and  dry  bulb,  33,  220. 

Thorp,  stall,  385. 

Thunder  storms,  associated  with  changes 
of  level  of  water  in  wells,  274  :  rela- 
tion to  ordinary  storms,  586,  588, 
origin  of,  588,  592  ;  progressive  move- 
ment of,  589. 

Thurston,    friction.    539. 

Ties,  for  cattle,  384. 

Tile,  essential  features  of,  291 ;  how 
water  enters.  292  ;  rate  of  percolation 
into.  292 :  Injured  by  frost.  291 :  clay 
suited  to  manufacture  of.  291 :  use  of 
collars  for,  292 ;  size  of,  299,  301. 


Index. 


603 


Tile  drains,  Influence  soil  ventilation, 
211 ;  fluctuations  In  rate  of  flow  from, 
270 ;  leveling  for,  312 ;  lor  ix.au 
drainage,  448. 

Tillage,  checks  concentration  of  alkali, 
98 ;  influence  of  on  development  of 
nitrates,  105 ;  to  conserve  soil  mois- 
ture, 182  ;  effectiveness  of  increased 
by  frequency,  187  ;  too  great  frequency 
undesirable,  189 ;  disadvantages  of 
late,  189 :  should  be  most  frequent  in 
spring,  19 ;  following  rains,  190, 
should  vary  with  season,  191  :  best 
time  for,  192  ;  subsoil  ing,  195  :  in- 
fluence of  on  soil  ventilation,  209 ;  in- 
fluence of  on  soil  temperature,  219, 
222  ;  objects  of,  223,  tools  for  earliest, 
225,  234  ;  for  later  cultivation,  226 ; 
to  cover  weed  In  row,  228 ;  garden 
cultivators  for,  230 ;  to  modify  soil 
texture,  231 ;  plow  as  a  tool  for,  238. 

Tilth,  importance  of  good,  233  ;  how  de- 
veloped, 233  ;  modified  by  plowing,  239. 

Timber,  strength  of,  330  to  334  ;  safe 
center  loads,  338 ;  selection  of,  338 ; 
construction  of  from  2-inch  lumber, 
339. 

Tires,  effect  of  width  on  draft,  436  ;  con- 
trol of  width,  481. 

Topography,  influence  of  on  soil  tempera- 
ture. 218. 

Tornadoes,  586 ;  relation  to  storms, 
586;  origin,  589. 

Towers,   hight   for  windmills,   534. 

Traces,  influence  of  slope  on  draft,  440, 
441,  492.  496. 

Traction,    see    draft. 

Trautwine,    332.    381. 

Tread   power,   499. 

Tresaguet,  type  of  road.  462. 

Triceps  muscle,  measuring  strength  of, 
489. 

Traube,  precipitation  membranes,  44. 

Tubes,  capillary  rise  of  water  in,  37, 
cause  of  variation  of  hight  of  water  in, 
161 ;  flow  of  water  through,  300. 

Turnip,  temperature  for  germination  of, 
213. 


Under  drainage,  Influence  of  on  sol!  ven- 
tilation, 210 ;  practice  of,  311 ;  tools 
for,  312  ;  determining  levels  for,  312  ; 
for  roads,  445  to  448. 

Units,  of  energy,  27 ;  of  heat.  28 ;  of 
work,  18,  27. 


Valentin,  respiration,  353. 

Valve,  slide,  of  steam  engine,  518 ;  of 
gasoline,  engine,  528. 

Vegetation,  influence  of  on  soil  ventila- 
tion, 211. 


Ventilation  of  soil,  lessened  by  rolling 
192 ;  needs  for,  204 ;  imperfect  in 
water  logged  soil,  205  :  may  be  exces- 
sive, 206 ;  processes  of,  207 ;  due  to 
changes  in  temperature,  207 ;  influ- 
enced by  changes  in  barometric 
pressure,  208  :  influenced  by  wind  suc- 
tion, 208 ;  influenced  by  percolation, 
209 ;  modified  by  tillage,  209 :  by 
underdraining,  210,  287,  290;  influ- 
enced by  vegetation,  211. 

Ventilation  of  farm  buildings,  350  ;  ma- 
terials to  be  removed  by,  350  to  353  ; 
lack  of  predisposes  to  disease,  352 ; 
amount  of  air  required  for.  353  to 
355  ;  forces  producing,  358  ;  types  of, 
355  to  365 ;  of  silos,  417  ;  of  box 
stalls,  387. 

Ventilating  flues,  capacity  of,  355 ;  es- 
sential features  of,  358 ;  location  of, 
359 ;  for  basement  stables,  355,  356, 
364 ;  openings  into,  360 ;  for  fresb 
air,  362  ;  construction  of,  363. 

Vierordt,    respiration,   353. 

Viscosity,  modified  by  dissolved  salts, 
106  ;  table  of  coefficients  of,  264. 

Voelcker,  nitrogen  In  soil,  82. 

W 

Wagner,  Illustration  of  symbiosis,  87,  ef- 
fect of  Chile  saltpeter,  88. 

Wagon,  draft  of,  434  to  443,  490. 

Walls,  solid  masonry,  346 ;  hollow  ma- 
sonry, 347  ;  brick  veneered,  347  ;  wood, 
348 ;  relation  of  to  floor  space,  366 ; 
rigidity  of  for  silos,  394. 

Waring,  denitriflcation,  90. 

Warington,  distribution  of  nitrogen  In 
soil,  84  ;  amount  of  nitric  acid  in  soil, 
84  ;  formation  of  nitric  acid  in  the  at- 
mosphere, 86  ;  denitriflcation  90. 

Water,  specific  heat  of,  29  ;  influence  of 
on  climate,  29  ;  use  in  cooling  iniik,  34  : 
amount  stored  in  rock,  51,  257  ;  work 
of  in  soil  formation,  54,  78 ;  flow  of 
through  sand,  123 :  conditions  of  In 
soil,  129,  130:  amount  of  required  by 
crops,  139,  140 ;  least  amount  re- 
quired by  different  yields,  141 ;  trans- 
piration of,  145 :  absorption  of  by 
roots,  147 ;  capillary  rise  of  in  tubes, 
161, — in  soils,  163  ;  amount  and  move- 
ment of  influenced  by  subsoil  ing,  197  ; 
influence  of  movements  of  on  soil  ven- 
tilation, 209  ;  amount  of  stored  in  soil 
and  rock,  255 ;  seepage  of  258,  259 ; 
laws  of  flow  through  porous  media, 
262,  264 ;  measurements  of  flow  of 
through  sands  and  sandstone,  264,  266, 
268 ;  fluctuations  in  rate  of  flr-w  of 
from  springs.  270,  271 ;  rise  and  fn'.l 
of  in  wells,  272 ;  temperature  of  In 
wells,  284:  how  it  enters  ti'e  drains. 
292 ;  movement  of  toward  tile  drains, 


604 


Index. 


298.  See  ground  water ;  In  expired 
air,  350 ;  relation  of  to  roads,  446 ; 
in  atmosphere,  558 ;  for  steam  boilers, 
517. 

Water   breaks,   449. 

Watering  stock  in  barn,  388 ;  trough, 
390;  tank,  390. 

Waters,  J.  H.,  draft  of  wagons,  436. 

Water  capacity,  of  soils,  114,  131,  132, 
134 ;  relation  of  to  surface  of  soil 
grains,  124 ;  increased  by  subsoiling, 
199. 

Waves,  of  solar  energy,  21 ;  kinds  of,  23  ; 
transparency  to,  24  ;  produce  chemical 
changes,  24. 

Weather,  forecasting,  554,  583 ;  of  dif- 
ferent wind  zones,  565,  changes,  578  ; 
influenced  by  storms,  580,  582. 

Weeder,  226. 

Weeds,  best  time  to  kill,  192,  224  ;  till- 
age to  destroy,  223,  loss  of  plant  food 
through,  224  ;  do  not  all  germinate  at 
once,  225  ;  best  tools  for  killing,  225 ; 
covering  in  row,  228 ;  jointer  for 
plowing  under,  249. 

Wells,  level  of  water  in,  255  ;  soils  and 
clay  supply  water  too  slowly  for,  257  ; 
fluctuations  in  flow  from,  270 ;  fluctu- 
ations in  level  of  water  in,  272  ;  es- 
sential features  of,  275 ;  capacity  of, 
275  :  geological  conditions  best  suited 
to,  276 :  depth  of,  283. 

Wheat,  exhaustion  of  soil  by,  80 ;  Roth- 
amstead  experiments  with,  82  :  water 
used  by,  140,  141 :  extent  of  root  de- 
velopment of,  150,  153 ;  temperature 
for  germination  of,  213. 

Wheels,  effect  of  size  on  draft,  437,  490  ; 
width  of  tire,  436,  481. 

Whitewashing,  silo  linings,  393,  402, 
403,  408. 


Whitney,  alkali  salts  limiting  plant 
growth,  93. 

Winds,  formation  of  soils  by,  63  ;  soil 
ventilation  influenced  by,  208 ;  prim- 
ary cause  of,  561 ;  of  the  globe,  562 ; 
zones  of,  563  ;  influence  of  earth's  ro- 
tation on,  564  ;  character  of,  564  ;  con- 
tinental, 566  ;  of  January,  567,  568 ; 
of  July,  567,  569  ;  monsoon,  570  ;  cy- 
clonic, 570  ;  anticyclonic,  572  ;  direc- 
tion of  in  forecasting,  579,  580  ;  rela- 
tion to  cold  waves,  582 ;  relation  of 
pressure  to  velocity,  532 ;  working 
power  of,  533 ;  unsteady  character  of, 
534. 

Wind-breaks,  to  conserve  soil  moisture, 
202. 

Windmill,  531;  pumping  by,  531,  535; 
grinding  by,  531,  536  ;  relation  of  di- 
ameter to  efficiency,  533  ;  towers  for, 
534. 

Wind  pressure,  force  in  ventilation,  346, 
358 ;  relation  to  velocity,  532 ;  rela- 
tion to  altitude,  532,  534 ;  relation  to 
temperature.  532. 

Wind  zones,  563  ;  weather  of,  565  ;  shift- 
ing of,  565. 

Windows,  efficiency  of,  348 ;  position  of, 
349. 

Winogradsky,  symbiosis,  88. 

Wollny,  influence  of  color  on  soil  tem- 
perature, 217. 

Wolff,  ash  of  crops,  79. 

Wolff,   A.  R.,  wind  pressure,  532. 

Wood  floors,  for  stables,  377. 

Work,  18  ;  units  of,  27. 


Z. 

Zero,  absolute,  23 ;  of  thermometers,  25. 


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King,  Franklin  Hiram 

A  text  book  of  the  physics 
of  agriculture. 


* 


BIO-AGRICULTURAL  LIBRARY. 
UNIVERSITY  OF  CALIFORNIA 
RIVERSIDE,  CALIFORNIA  92502 


